Alcohol is hands down terrible for the body. I'm becoming more and more convinced from scientific studies and my own observations that no amount, not even one glass of wine a night, is physically beneficial.
It's the psychological benefits outlined here that are much harder to persuade away - mediator of anxiety, social lubricant, escape into a little bit of fun. Nonetheless, for me, the physical toll is just not worth it anymore.
Marijuana is even more difficult to dissuade. There is a physical toll to excessive smoking, but it's much less pronounced than alcohol, and seems largely non-existent when consumed in moderation, the equivalent of a glass of wine a day. The only inarguable cost is the time one isn't sober and able to be socially/economically/physically productive.
Nonetheless this loss of time, too, seems more and more valuable to me, and my marijuana intake is naturally declining.
As time goes on the statistics on alcohol consumption and substance addiction make more and more sense to me: a third of Americans don't drink AT ALL, most drink less than a glass a week, and most drug addicts naturally quit without intervention. Most of us come to the truth eventually, it seems.