[tghw]

I would guess it has to do with both the way enough people have behaved in the past while drinking heavily, as well as the nearly unassailable excuse of "I didn't mean it, I was just a little tipsy."

Note that at a conference, even at the after hours events, you're still at a professional event, surrounded by peers and colleagues, not friends.

That said, I certainly enjoy partaking, just not heavily when in that environment.