In college, I was a part of two very different scenes (well, not as different as I thought, but stay with me). I was a member of a fraternity, and I was active in a religious group called TNT. It was a non-denominational protestant Christian group. I say they aren't all that different for two reasons. First, when joining a fraternity, a majority of the young men have one unmistakable goal in mind -- to meet young women. I joined TNT for a similar reason, and I'm sure other guys did, too. In fact, I think I joined the Arbor Day club, or some such thing, for the same reason. Oh, and the Biology Club. But I'm getting away from my original point here.
My point is this. While alcohol obviously melts away inhibitions, I'm pretty sure the lateness of the hour also makes a huge difference.
At fraternity parties, where much alcohol was consumed at late hours, inhibitions tended to fall by the wayside. Any emotions, whether elation, sadness, anger, sexual attraction, whatever, tend to come out more.
Go with me now to a nighttime activity during a weekend getaway with TNT. No alcohol was consumed, and yet by the time it got late and they were passing around the mic for folks to share their experiences, the responses were much more emotional than they were earlier in the day. Finally, after a couple of people had become teary-eyed blubbering bags of flesh, the guy leading the session stopped the sharing and suggested everybody go to their respective sleeping quarters.
By the time one has a full week of classes, work, or a combination of both, then feels the stress of social situations, the night can find that person severely fatigued physically and mentally. That mental exhaustion causes one's capacity for resistance to fall. Self-discipline often takes a backseat to self-expression and acting on a whim. Why do you think infomercials are played mostly late at night? Because marketers know that the consumers' resistance is down at that late hour. I've never read a study on it, but haven't you ever ordered anything late at night, or written a heated e-mail (or blog post) late at night, without having had anything to drink, only to realize after waking that you had made a mistake?
Consider whether you think a party at noon, with alcohol, would result in as many one-night stands as does a party that goes into the wee hours of the morning? Likewise, do you think that as many Ronco products would have sold if the infomercials for them would have played during primetime?
I'm no expert, and I'm sure someone will dispute this (if anyone's reading it). I'm just sayin'. Tha's all. Then again, I am writing this late at night.