> If we invested USD$10-15 billion a year (as compared with ~USD$50 billion on "drug enforcement") into the resources required to provide treatment for anyone who wants/needs it, and legalize/regulate all "drugs", will save money, increase economic output and improve social cohesion.

I don't think there is much evidence for that (nor against it). One country that has tried something like that is Portugal and from what I can tell it has worked moderately but not spectacularly well. The problem with assuming that the US would have the same outcome is that the US shares a porous border with a part of the world heavily involved in drug trafficking and the US is a much larger country and larger consumer of narcotics, so the demand effects are hard to compare with Portugal.