Look up the studies for areas where it is decriminalized and areas where certain drugs are legal. Portugal would be a good place to start. Let Google be your guide.
I understand what you're doing, shifting the work to me, but it is generally courteous in a discussion to provide an argument to support your points. Why should I do the work for you and then let you sit back and pick at my arguments? I am not making a positive statement either way on the issue. You are the one that has made the assertion that illegality of heroin is the primary causal factor in it's being harmful, so you are the one that has the onus to provide supporting evidence for your claims.
I'm being downvoted because I started this off being snarky and, frankly, an ass to you. I think my points are still valid but it's not a kind way of communicating them, and for that I apologize.
