I have had first hand experience of dealing with immediate family members and friends who have been addicted to legal drugs like alcohol, and illegal drugs like meth. The impact that addiction can have on others who are not addicts is quite disturbing and I have had a mild experience to say the least. I have even struggled with my own addictions.
I think drugs like marijuana is ok, but a drug like meth oh no that's just not good at all. Even alcohol I question a lot, even a quick google search suggest 40% of murders are committed in the USA while under its influence.
Also there are questions about how drugs can be legally sold, I read an article the other day that San Francisco was stopping tax hikes on marijuana stores because of the rise of the illegal marijuana trade. When governments get involved the outcomes are not always as expected. Would legalizing and taxing cocaine for example really stop the mass murders and gang violence in South and Central Americas.
Decriminalize, treat the people with addiction rather than locking them up for possession, educate, etc. That's my thinking.