Okay, here's the thing.
Legally, it's rape if the person is intoxicated. Legally, you can't consent while intoxicated, just like you can't legally consent when you're 4 or when you have a gun held to your head. This is all well and good as far as it goes, as slipping someone a few pills should ALSO be considered rape... you don't think straight.
So legally, if someone cries foul after the fact you're screwed... even if you were drunk as well. Technically this is the case even if you and your SPOUSE get drunk... and this is where a bit of the fear comes in.
In this case, though, you have a problematic scenario... lots of people (though certainly not all) get drunk for the express purpose of meeting people and having sex. If you go with that intention, in a way you've consented prior to being drunk, and only an explicit "No" from you should override that. Otherwise, you have the very real danger of someone who's just as drunk as you, who went to the bar for the same reason you did, to have some fun, getting put into jail because you had a change of heart when you got sober again.
Incidentally, I'd be interested in seeing how a place with waiver forms at the door to that effect would hold up... certainly with a clause that verbal or physical refusal of sex would void it, but something along the lines of, "This is a hook-up bar. I come here with the intention of getting laid, and I hereby consent to any sexual contact that seems like a good idea to me at the time." People who didn't feel that way could go to different bars, where there would not be that assumption that you're going home with somebody else.
Now personally, I don't drink, nor do I engage in casual sex. Neither is my thing. However, both are perfectly valid choices, and I think that things could be made better for all by just making some things a little bit clearer... perhaps with the segregation of "hook-up, pre-consent" bars and the normal kind... with some sort of supervision in place at the other bars to make sure that hook-ups DIDN'T happen, no matter how consensual they appeared to be.