The thing is, they already are. Excessive drinking at a friends house is so normalized here, it's become background. The police might pull you over if you're swerving all over the road on the way back home, but usually they wont. Adding weed to that mix of "normal" background behaviours is going to improve that? I don't think so.
And I'm not saying prohibit all vices. People need their release - of course they do - but rather than encourage new addictions behind closed doors, can't we just make it easier for people to hang out in public at night?
Again, it's not binary for me, despite these increasingly polarized times we live in. No one should undergo the same prison sentencing as rapists just for carrying a potentially addictive and life-altering substance, but we shouldn't also (in my opinion) just open the gates and let this substance into foray of our daily lives.
Hell, alcohol shouldn't be so freely dispensed as it (see: russia's entire history), but we do it anyway. Adding another substance just seems like a step backwards for me.