I do see your point, all the more clearly for being calmly put. You're right in what you say, but miss out a few important factors.
Yes, identity politics can cause unnecessary divides in the greater community. At its worst extremes, you can get people falling out over ridiculously arbitrary things, like which football team they support, which postcode they live in, or what anime they watch. I wouldn't deny that some gay activists would like to separate themselves off from the straight world, and that this is not the way to go.
However, there is also the matter of specialization. The amateur astronomy community aren't trying to divide society, but they do have their own magazines, websites, discussion boards, meets and conventions. This is because not everybody shares their interests. If you built a home-grown five telescope array up in the highlands of Scotland and spotted and plotted a 50-metre wide asteroid that wasn't on any of the official databases, the mainstream press would be seriously underwhelmed, and would be unlikely to cover you and your boring bit of rock. By contrast, Astronomy magazine would probably give you a two-page spread at least, along with an effusive write-up on "the advanced amateur matching the big, funded agencies at their own game".
While the situation has improved over the years, there is still a lot of hostility towards homosexuals. It's been driven out of the mainstream a bit, and underground a bit, but it's still there. Hence a desire to create places where they don't have to worry about this, and support networks with supporting voices. Sometimes these don't need to be created - at our workplace we have had two parties for gay colleagues who were getting hitched to their partners. I don't know if there were any homophobes among our colleagues, but if there were, they kept quiet about it. There are plenty of places where homosexuals will get a hostile reaction, and there are also plenty of places where homophobes will get a hostile reaction. You can't really blame homosexuals for wanting to create more of the latter.
It's not as if this applies to homosexuals alone. There are other people who have to watch where they hang out or reveal themselves. Cross-dressers, train-spotters, morris dancers, BDSMers, furries, philatelists (USA only) - they all have places where they would be subject to ridicule or hatred, and other places where any haters would find themselves outnumbered.
Maybe, one day, Martin Luther King's dream will come true, and there will be no need for different groups to band together like this. Maybe the gay media and blogosphere will be able to shrink down and just cover the few items that are of interest to homosexuals only. Maybe the BDSMers will be able to go about their business in full bondage gear, and football hooliganism will stop through lack of interest. Maybe, one day, but it's a long way off. We still have people getting kicked to death by idiots because they look different, and people like Anonymous C***** Tuesday 14th April 2009 11:52 GMT calling for book burnings just because he/she/it doesn't like the material. While that goes on, there will be a gay blogosphere, and it will resist all attempts to make it go away.
By the way, it's not a problem if you just don't like homosexuality - or Marmite, for that matter. You're not expect to partake of Marmite just because you're in a Marmite-loving crowd, or even look at Marmite if you don't want to. But verbally abusing or attacking someone because they have Marmite in their shopping trolley is right out. Not even if your church tells you that Marmite is the Devil's soil. (Although you are allowed to use reasonable force against anyone who smears Marmite on you without your consent.) Your friends ought to respect your preferences, and yes, they should choose whether to keep their preference in sandwich spread a private matter. However, as a rational adult in the modern world, you ought to be able to handle the knowledge that they have Marmite in their cupboard, provided they keep the door shut when you visit.