It's interesting, I thing it's because heterosexual culture is shoved in the face of gay people, night clubs are almost always exclusively heterosexual.
The may be predominantly hetero, but that's because the population at large is also predominantly hetero. That's not really the fault of the clubs, that's just the way it is. It isn't like you go down the street and see "straight bars" and "gay bars." It's always just "bars" and "gay bars." Not that straights aren't allowed in gay bars, just as gays aren't banned from straight bars.
The media is very heterosexual in it's output
Again the majority of the populace is straight, so that's what the majority of media with be about. Although we are seeing more gay/bi characters in tv, and movies now than we have in the past.
, so having somewhere you can go and just feel relaxed and open knowing that people around you are also homosexual, and open to the same feelings as you it can be great. It's not to segregate between "us and them" it's more to have something that "we" can call our own, just as heterosexuals seem to have....
This concept may work in a setting like a gay bar or club, but it doesn't apply to something like a gay pride parade. In that case it isn't about having something to call their own, but rather a method of exposing their culture to others. And in this case it only works because gays are in the minority. If anyone hosted a straight pride parade someone would make a shit fit!
I think it's also because although we want complete equality, the fact is that homosexuals are a minority and as a result when you see two guys or girls kissing in a night club, people look like it is something unusual.
I'd equate it to the fact that women like having women only gyms because they feel more comfortable without men looking at them. It's not to segregate its to be with the same kind of people.
IMO "being with the same kind of people" is the same as segregation. That's like saying blacks were never segregated in America, it was simply white people hanging out together. (OK maybe a bit of an exaggeration, but you get the idea).