I have no idea if there is a correlation between cities that have legal weed and higher rates of homelessness/opiod addiction, but the part that doesn't really make a lot of sense to me is like, heroin, meth, et. al are already illegal so these folks are already willing to break the law, i don't see how weed being legal would really matter.
That's kind of like saying if i'm going to be a bank robber i'm going to move to Montana so if I end up in a high speed chase with the cops they can't bust me for speeding.