I think you've made some excellent points, but you can't simultaneously deny the existence of negative societal externalities caused by individual drug use while acknowledging that the usage of drugs (including alcohol, tobacco, and excessive eating) imposes a cost onto society in the form of [just one example] increased healthcare spending.

I think my particular stance is that the war on drugs is a massive failure that props up prices, lowers quality, and destroys the lives of many young non-violent "offenders." This is probably quite similar to your position, but I think the primary difference is that I would not advocate lifting the prohibition against drugs like heroin, which can supposedly turn a person into an addict within a few sessions.

I think my position is ultimately something like this:

Should the state lock someone up for using heroin? No, it's their money and their body.

Should the state lock someone up for using heroin and then committing a crime? Yes, because of the crime.

Would the legalization of heroin cause an increase in number of people committing crimes? Yes, because of its addictive potential and the extremely difficult/potentially fatal withdrawals.

Whether or not that would actually be the case, I can't say.