I don't think of "prevented" as a binary status. It's clear that at least some are prevented and the others are simply taken off the streets, making some of the aforementioned issues smaller, with certain other tradeoffs. I do not expect there to be a perfect solution any which way society goes about this. I have not seen much debate well informed enough to give more than opinions about the actual magnitude of many of the costs and tradeoffs, though I am interested in some of the talk about decriminalization (which is sometimes confused with legalization) combined with expanded addiction treatment programs.