I'm always surprised that this topic doesn't get more posts on here. I mean, alcohol is well documented to cause, erm, blood flow problems and from this side of the fence, why would I have wanted to sleep with someone who doesn't even seem to like me?
For me, resentment has a major effect on my libido and my ability to let my guard down and be vulnerable with a person. Added to this, the demands that an alcoholic makes in day to day life, coupled with having to pick up the slack where they drop the ball, mean that sex can become just another chore. Why these people don't realize that foreplay starts outside the bedroom and that they'll get more action if they just started being a bit nicer, I will never understand. Whining and demanding is a big fat FAIL on the seduction front, alcoholic or not.
And, of course, it's just something else for them to build their own resentment about, to make it your fault and give a fat, juicy reason to drink.