This is in response to this and I think he was responding to this. There is one thing I've noticed that Mr. Brunomac seems to have missed. The majority of people who don't allow drinking at their games are under 33 in age(or are involved in other forms of gaming).
It really is a bit of an age/culture war. The younger generations may be considered lazy and may have ADHD, but they're competitive when it comes time to have fun. In video games we have gamer/achievement scores, in board games and war games there are clear winners and losers, and in adventure RPGs of all types there is a competition mentality between DMs and Players. Oh sure, there are plenty of hippy storytellers all singing kumbaya around a campfire while crafting their shared narrations, but a lot of groups out there still have a competitive mindset to them.
Where does this competitive streak come from? Partially from the rules being used. It's a "dirty" word but a lot of players realize that they have to optimize their characters. This is just as true in oldschool games as it is in new games like Pathfinder or 4e.
Two reasons exist for this; The first is the oldschool meatgrinder. Levels 1-3 in most oldschool games are where most characters tend to die. The tendency of most players then is to make as powerful a character as possible to survive this winnowing. The second reason is peer pressure. Most people playing in successful multiplayer games realize that the challenges they overcome as a group(be it raid group or adventuring party) is a result of each character and each player being at the top of their game, so there's a certain stigma attached to playing in a sub-optimal manner. Even if nobody enforces it, most players in these competitive games feel a certain amount of guilt if they choose to play with a less powerful character.
So, whether you like it or not, we have a large number of highly competitive gamers out there who view the playing of games as a means of testing their own minds and "gamer skills" to the limit. I'm fairly certain nobody can argue against the fact that after a certain point, drinking does hamper the ability to think clearly.
It has been my experience, that those gamers under 33 years of age who choose to drink, tend to be disruptive to the game and tend to take away from everyone's fun when they're drinking openly. For whatever reason, this group of people has a tendency to not drink responsibly while gaming. This makes it fall on the host, raidleader, or DM to figure out a way to control the problem.
The easiest way to do this is to ban drinking. Realistically, this is impossible, but doing so does seem to control the outbursts and cause the drinkers to drink in moderation because they have to keep it secret. This is generally considered the best course of action when the group is not necessarily all friends outside of the game.
The second option, and the one I favor at face-to-face games, is host as bartender. This is harder to do as certain individuals may end up being offended when the host starts cutting people off because they're at the agreed upon limit. As such individuals rarely stay silent about their complaints, this ends up causing the game to be put on hold while the entire group ends up arguing for or against person X having another alcoholic beverage.
So to Brunomac, it's not a matter of being prudish, it's because a large enough number of gamers are drinking to the point where it's taking the fun away from the other players, and becoming a problem that has to be dealt with. I envy the fact that you are able to allow drinking at your games, and hope to one day find a group that is able to do so without causing problems, but at this point, I think many of us have to deal with the reality that our current choice in gaming companions and styles do not mix well with the presence of alcohol.