Well, let me try to be Larry Logical.
There are issues that come up from time to time that are either unique to the gay community or happen more often in that community then others. They are still a group of people that are isolated or marginalized in large parts of our society.
As an easy example, I don't have to worry about which state I can marry in or how someone in a theme park will look at me when I embrace my significant other. I'm sure there are many more but I will let someone from that community speak about them if they feel fit.
Now, is it true that often times the majority is made to feel bad about having pride in themselves? I would argue yes. Having strait pride doesn't mean you are anti gay any more then having gay pride means you are anti strait. Having white pride does not mean you are anti minority any more then having black pride is anti anything not black. Are there some people of all of those that take their pride to the extreme? Yep, there is. When someone proclaims their pride in being white/strait/Christian as a way of demeaning or intimidating those that are non-white/gay/non-Chrisitian it goes from being real pride to being passive aggressive bullying.
All of that previous paragraph being said (or typed), there is a difference between being the in the majority and in the minority. We don't need the separate space (I have no idea what term to use for this) because our interests are addressed in "normal" society or on the "regular" boards. It is just a logical side effect of being the majority.
Even if everyone wanted to get along as one big happy group that accepted each other there would still have to be a way for people who weren't represented in the majority to address their race/sexuality/religious specific issues because the nature of being in the minority means your needs aren't always addressed in the majority. Sometimes this is on purpose and some times it is just a side effect of numbers.
Unfortunately far too many people haven't figured out that different isn't better or worse, it is just different.
Of course everything above is kind of irrelevant because the boards are a private thing owned by private people who will do with it what they please.