I broke my humeral mid-shaft during a set of weighted dips. Torquing the arm or any kind of twisting with that much weight can be risky business and the tendency might occur for some when they are struggling with the weight on a movement like that is to torque or twist their arms some.
They are a great lift but my preference has returned to flat barbell bench for obvious reasons. Dips have unfamiliar mobility requirements for some lifters to do safely weighted.
I don't have any qualms recommending those who can perform them safely to do weighted dips though, if you refuse to do a movement just because someone you know injured themselves doing it eventually you won't be doing anything at all.