This is exactly why nobody should never have sex, because then they might try sodomy.

Could you cite the study? Since personal experience is apparently credible in this argument and we don't need to go and survey >1008 people [see: Law of Large Numbers], I don't know any of my friends who use marijuana that do anything harder than alcohol.   What exactly is "often" by the way?  Sure, we've all heard these claims in health class, but I haven't found a single credible study yet.

I don't think anyone is smoking marijuana and thinking "hey, you know what I need?  Some heroin, yeah, that'd really do the trick right now."  And why is it that only marijuana gets a bad rap for this?  Why not alcohol, which has been proven to be a harder drug.