I don't read mythrwy as blaming those who are already addicted and can't fight their drug habit, but rather those who start taking drugs even when they should be able to see the consequences. (Some quotes [emphasis mine]: "the personal decision to use hard or addicting drugs is something of a moral failing.", "it is a vice in which people for the most part, at least initially, have some choice.")

Shaming doesn't help the addicts, and probably hurts them by making help less available, but it absolutely helps those people who do not yet have a drug habit. The stigma definitely helped me decline when a bunch of my friends started with marijuana (and I'm sure some did worse, but by then we had become distant).

Although decriminalization is the right move to help addicts, it will also have an effect on non-users who were curious but shied away from doing something illegal and getting in trouble. Personally, I think drugs should be available on a prescription for everyone who actually needs them, but off-limits to those who just want to try them out.

Regarding your aside: I'm not sure what kind of dystopia you imagine a "healthy environment" would be. I interpreted it as making sure that people can feel happy without drugs, e.g. by giving them a stable source of income, fostering community and so on. Do you disagree that those would be a good thing?