I'll have to disagree strongly with you and
@SkankHunt on this. It isn't just the reddit crowd. I've fielded this question on multiple forums and it isn't an issue unique to reddit.
Many people suck at unit conversions and understandably so. Hence, informed people and people making drugs should simply not think its cool and sufficient to use units of mass (mg) in place of the correct units for concentration (mg/ml). Period.
This isn't high school / let's see how cool we can be for acting like a dumbass. People are injecting these drugs and the least that could be done by the people who profit from this stuff is to use correct units. But maybe some people like their drug manufacturer/dealer to be "cool" instead of correct. Different strokes.
Clean up the product listings.