And until we can find a pair of genetically identical twins, separated at birth, one living in upper-middle-class and the other living in a ghetto, who are willing to participate in this experiment, it will remain a theory.

Dang, how many times do I have to apologetically qualify this example with adjectives like "artificial"?

With respect to some people will be more genetically predisposed to become addicted than others. It's just in that culture, they're more likely to get more doses of the drug, which will trigger addiction even in those not predisposed to it. I *think* we are strongly agreeing. I just can't tell.

My example and theory uses contrived single-person examples where no truly exact comparison is possible.

Let's slice it another way - a more legitimate population-based approach: Let's conduct a highly statistically significant study of crack addiction among women aged 17-25 in all affluent suburbs in the U.S. and in all inner-city neighborhoods that meet certain poverty criteria. We'll stratify the results by suburb vs. inner-city. If we observe a significant difference, and I'm guessing we will, we'll then call the biologists and geneticists and leave it to them to explain it!

Again, I think that this is the kind of stuff that addiction "experts" still argue about all the time. I'm guessing that plenty of academic experts have done pop-based studies like that, probably go to a lot of trouble to control for factors like race, age at first exposure, nativity, family size, etc. but have a challenging time with the analysis. If I wasn't so lazy, I'd go do a literature review.