The parent comment was complaining that legal consumption made the environment threatening.
>maim and kill users, push users into poverty, and generate and push the externalizes of drug use onto the rest of society.
None of these appear to hinge on decriminalization vs. legalization. Alcohol, for example, maims and kills users, pushes severely addicted users into poverty, and externalizes the problems of its use onto society.
Use went down during prohibition, use went up during legalization. So in effect you're proposing we increase these problems as related to meth and other hard drugs.
(This is not an argument for prohibition of alcohol, it is merely listing the cons of legalization)