Bertrand Russell had this to say on the topic:
The Existence of God
To come to this question of the existence of God: it is a large and serious question, and if I were to attempt to deal with it in any adequate manner I should have to keep you here until Kingdom Come, so that you will have to excuse me if I deal with it in a somewhat summary fashion. You know, of course, that the Catholic Church has laid it down as a dogma that the existence of God can be proved by the unaided reason. That is a somewhat curious dogma, but it is one of their dogmas. They had to introduce it because at one time the freethinkers adopted the habit of saying that there were such and such arguments which mere reason might urge against the existence of God, but of course they knew as a matter of faith that God did exist. The arguments and the reasons were set out at great length, and the Catholic Church felt that they must stop it. Therefore they laid it down that the existence of God can be proved by the unaided reason and they had to set up what they considered were arguments to prove it. There are, of course, a number of them, but I shall take only a few.
The First-cause Argument
Perhaps the simplest and easiest to understand is the argument of the First Cause. (It is
maintained that everything we see in this world has a cause, and as you go back in the
chain of causes further and further you must come to a First Cause, and to that First
Cause you give the name of God.) That argument, I suppose, does not carry very much
weight nowadays, because, in the first place, cause is not quite what it used to be. The
philosophers and the men of science have got going on cause, and it has not anything like the vitality it used to have; but, apart from that, you can see that the argument that there must be a First Cause is one that cannot have any validity. I may say that when I was a young man and was debating these questions very seriously in my mind, I for a long time accepted the argument of the First Cause, until one day, at the age of eighteen, I read John Stuart Mill's Autobiography, and I there found this sentence: "My father taught me that the question 'Who made me?' cannot be answered, since it immediately suggests the further question `Who made god?'" That very simple sentence showed me, as I still think, the fallacy in the argument of the First Cause. If everything must have a cause, then God must have a cause. If there can be anything without a cause, it may just as well be the world as God, so that there cannot be any validity in that argument. It is exactly of the same nature as the Hindu's view, that the world rested upon an elephant and the elephant rested upon a tortoise; and when they said, "How about the tortoise?" the Indian said, "Suppose we change the subject." The argument is really no better than that. There is no reason why the world could not have come into being without a cause; nor, on the other hand, is there any reason why it should not have always existed. There is no reason to suppose that the world had a beginning at all. The idea that things must have a beginning is really due to the poverty of our imagination. Therefore, perhaps, I need not waste any more time upon the argument about the First Cause.
The Natural-law Argument
Then there is a very common argument from natural law. That was a favorite argument
all through the eighteenth century, especially under the influence of Sir Isaac Newton and his cosmogony. People observed the planets going around the sun according to the law of gravitation, and they thought that God had given a behest to these planets to move in that particular fashion, and that was why they did so. That was, of course, a convenient and simple explanation that saved them the trouble of looking any further for explanations of the law of gravitation. Nowadays we explain the law of gravitation in a somewhat complicated fashion that Einstein has introduced. I do not propose to give you a lecture on the law of gravitation, as interpreted by Einstein, because that again would take some time; at any rate, you no longer have the sort of natural law that you had in the Newtonian system, where, for some reason that nobody could understand, nature behaved in a uniform fashion. We now find that a great many things we thought were natural laws are really human conventions. You know that even in the remotest depths of stellar space there are still three feet to a yard. That is, no doubt, a very remarkable fact, but you would hardly call it a law of nature. And a great many things that have been regarded as laws of nature are of that kind. On the other hand, where you can get down to any knowledge of what atoms actually do, you will find they are much less subject to law than people thought, and that the laws at which you arrive are statistical averages of just the sort that would emerge from chance. There is, as we all know, a law that if you throw dice you will get double sixes only about once in thirty-six times, and we do not regard that as evidence that the fall of the dice is regulated by design; on the contrary, if the double sixes came every time we should think that there was design. The laws of nature are of that sort as regards a great many of them. They are statistical averages such as would emerge from the laws of chance; and that makes this whole business of natural law much less impressive than it formerly was. Quite apart from that, which represents the momentary state of science that may change tomorrow, the whole idea that natural laws imply a lawgiver is due to a confusion between natural and human laws. Human laws are behests commanding you to behave a certain way, in which you may choose to behave,
or you may choose not to behave; but natural laws are a description of how things do in
fact behave, and being a mere description of what they in fact do, you cannot argue that there must be somebody who told them to do that, because even supposing that there were, you are then faced with the question "Why did God issue just those natural laws and no others?" If you say that he did it simply from his own good pleasure, and without any reason, you then find that there is something which is not subject to law, and so your train of natural law is interrupted. If you say, as more orthodox theologians do, that in all the laws which God issues he had a reason for giving those laws rather than others -- the reason, of course, being to create the best universe, although you would never think it to look at it -- if there were a reason for the laws which God gave, then God himself was subject to law, and therefore you do not get any advantage by introducing God as an intermediary. You really have a law outside and anterior to the divine edicts, and God does not serve your purpose, because he is not the ultimate lawgiver. In short, this whole argument about natural law no longer has anything like the strength that it used to have. I am traveling on in time in my review of the arguments. The arguments that are used for the existence of God change their character as time goes on. They were at first hard intellectual arguments embodying certain quite definite fallacies. As we come to modern times they become less respectable intellectually and more and more affected by a kind of moralizing vagueness.
The Argument from Design
The next step in the process brings us to the argument from design. You all know the
argument from design: everything in the world is made just so that we can manage to live in the world, and if the world was ever so little different, we could not manage to live in it. That is the argument from design. It sometimes takes a rather curious form; for instance, it is argued that rabbits have white tails in order to be easy to shoot. I do not know how rabbits would view that application. It is an easy argument to parody. You all know Voltaire's remark, that obviously the nose was designed to be such as to fit spectacles. That sort of parody has turned out to be not nearly so wide of the mark as it might have seemed in the eighteenth century, because since the time of Darwin we understand much better why living creatures are adapted to their environment. It is not that their environment was made to be suitable to them but that they grew to be suitable to it, and that is the basis of adaptation. There is no evidence of design about it.
When you come to look into this argument from design, it is a most astonishing thing
that people can believe that this world, with all the things that are in it, with all its
defects, should be the best that omnipotence and omniscience have been able to produce in millions of years. I really cannot believe it. Do you think that, if you were granted omnipotence and omniscience and millions of years in which to perfect your world, you could produce nothing better than the Ku Klux Klan or the Fascists? Moreover, if you accept the ordinary laws of science, you have to suppose that human life and life in general on this planet will die out in due course: it is a stage in the decay of the solar system; at a certain stage of decay you get the sort of conditions of temperature and so forth which are suitable to protoplasm, and there is life for a short time in the life of the whole solar system. You see in the moon the sort of thing to which the earth is tending -- something dead, cold, and lifeless.
I am told that that sort of view is depressing, and people will sometimes tell you that if they believed that, they would not be able to go on living. Do not believe it; it is all
nonsense. Nobody really worries about much about what is going to happen millions of
years hence. Even if they think they are worrying much about that, they are really
deceiving themselves. They are worried about something much more mundane, or it may merely be a bad digestion; but nobody is really seriously rendered unhappy by the
thought of something that is going to happen to this world millions and millions of years hence. Therefore, although it is of course a gloomy view to suppose that life will die out - at least I suppose we may say so, although sometimes when I contemplate the things that people do with their lives I think it is almost a consolation -- it is not such as to render life miserable. It merely makes you turn your attention to other things.
The Moral Arguments for Deity
Now we reach one stage further in what I shall call the intellectual descent that the
Theists have made in their argumentations, and we come to what are called the moral
arguments for the existence of God. You all know, of course, that there used to be in the old days three intellectual arguments for the existence of God, all of which were disposed of by Immanuel Kant in the Critique of Pure Reason; but no sooner had he disposed of those arguments than he invented a new one, a moral argument, and that quite convinced him. He was like many people: in intellectual matters he was skeptical, but in moral matters he believed implicitly in the maxims that he had imbibed at his mother's knee. That illustrates what the psychoanalysts so much emphasize -- the immensely stronger hold upon us that our very early associations have than those of later times.
Kant, as I say, invented a new moral argument for the existence of God, and that in
varying forms was extremely popular during the nineteenth century. It has all sorts of
forms. One form is to say there would be no right or wrong unless God existed. I am not
for the moment concerned with whether there is a difference between right and wrong, or whether there is not: that is another question. The point I am concerned with is that, if you are quite sure there is a difference between right and wrong, then you are in this situation: Is that difference due to God's fiat or is it not? If it is due to God's fiat, then for God himself there is no difference between right and wrong, and it is no longer a significant statement to say that God is good. If you are going to say, as theologians do, that God is good, you must then say that right and wrong have some meaning which is independent of God's fiat, because God's fiats are good and not bad independently of the mere fact that he made them. If you are going to say that, you will then have to say that it is not only through God that right and wrong came into being, but that they are in their essence logically anterior to God. You could, of course, if you liked, say that there was a superior deity who gave orders to the God that made this world, or could take up the line that some of the gnostics took up -- a line which I often thought was a very plausible one -- that as a matter of fact this world that we know was made by the devil at a moment when God was not looking. There is a good deal to be said for that, and I am not concerned to refute it.
The Argument for the Remedying of Injustice
Then there is another very curious form of moral argument, which is this: they say that
the existence of God is required in order to bring justice into the world. In the part of this universe that we know there is great injustice, and often the good suffer, and often the wicked prosper, and one hardly knows which of those is the more annoying; but if you are going to have justice in the universe as a whole you have to suppose a future life to redress the balance of life here on earth. So they say that there must be a God, and there must be Heaven and Hell in order that in the long run there may be justice. That is a very curious argument. If you looked at the matter from a scientific point of view, you would say, "After all, I only know this world. I do not know about the rest of the universe, but so far as one can argue at all on probabilities one would say that probably this world is a fair sample, and if there is injustice here the odds are that there is injustice elsewhere also." Supposing you got a crate of oranges that you opened, and you found all the top layer of oranges bad, you would not argue, "The underneath ones must be good, so as to redress the balance." You would say, "Probably the whole lot is a bad consignment"; and that is really what a scientific person would argue about the universe. He would say, "Here we find in this world a great deal of injustice, and so far as that goes that is a reason for supposing that justice does not rule in the world; and therefore so far as it goes it affords a moral argument against deity and not in favor of one." Of course I know that the sort of intellectual arguments that I have been talking to you about are not what really moves people. What really moves people to believe in God is not any intellectual argument at all. Most people believe in God because they have been taught from early infancy to do it, and that is the main reason.
Then I think that the next most powerful reason is the wish for safety, a sort of feeling
that there is a big brother who will look after you. That plays a very profound part in
influencing people's desire for a belief in God.