I can't play sober anymore. Obviously if you don't feel comfortable don't do it, but there are a few positives people are missing:
1. This may just be a me thing, but when I'm just concentrating on playing poker I get extremely bored. I used to play up to 16-20 tables online, so sitting there playing at a slow table can be incredibly boring and I actually play way looser when I'm not drinking/chatting with other people.
2. It's easier to get action when drinking. First off they don't realize how tight you're playing they just think of you as the drunk guy/girl, and even if they do think you're playing tight fish are a lot more likely to want to play with you/pay you off if you're drinking and having fun with them. I had one guy call a $450 preflop raise blind at a 5/10 table because I was his "nemesis". He then called off the other 2k on the flop with his underpair. He probably knew he was behind (I had AA lol), but the money was nothing to him and he was willing to spend that on playing with a "fun" player. The nits with the headphones and sunglasses he was much less happy to splash around with.
3. If you've been playing the game for awhile you're probably not going to all of a sudden start doing terrible things while drinking. I definitely loosen up and 3-bet a bit more than optimal on occasion but it's not like I'm going to start calling the river with J high.
Anyway like I said not applicable to everyone and if you don't feel comfortable drinking and playing definitely don't, but definitely some positives to weigh against the negatives of impaired decision-making.