We actually played in a pub for several months when we were wild, young and had nowhere else to play, so it is not overly surprising that we are prone to having a drink or two. And as we are still pretty much the same group and we have always socialised with each other over drink, roleplaying night has always included drink.
I will always have a bottle of wine and a beer or two, or maybe a fair whack of Stoli. Only one person of our group does not imbibe much, and that is because he drives.
Drink can be a pain in the arse when players get too drunk, but you know what so can a lot of other things. When a player is silent, or does not know (and will not learn) any of the rules, or is just feuding with another player. Booze might sometimes make our campaign worse but a lot of things do that. It certainly makes the night better for me as a social event.
As to drugs, at the moment I would have to refuse, as a non smoker for nearly 15 months I would be keener on the fine tobacco than anything else. God I miss smoking so badly. If anyone else wanted to then I would be OK with it, they are all responsible adults who are my friends. As we live in the middle of nowhere like we do we don't play with other groups or players, I may have had different views if I had to deal with drunken/stoned people that I did not know and like!