Does supply play a role in addiction? Opportunity?

I'm not sure exactly what you're asking, but to your point in another comment, I have some sympathy to setting an 'addiction bar' and prohibiting drugs above that bar. Of course, the biggest issue with all these discussions is that, by any objective measure of harm/addiction, alcohol ranks right up there alongside heroin, meth, etc.

But all of this is a tangent to the 'war on drugs' which doesn't even begin to address the issue sensibly.