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So I generally understand where you're coming from, but at the same time I understand why these people are outspoken. Lets just sort-of break down the argument a bit and go through each level step-by-step.
Exclusivity: The first point you made is the idea of exclusivity, you said "I understand that you maybe want to meet others who are also gay/bi/whatever, but is it really fair to be exclusive and act like it makes you part of some sort of special club?". Now, as you may know, some LGBT people have a very tough time with their sexuality. Their parents may disagree with them, their friends may disagree with them, they may be bullied, threatened or even assaulted. I know at least two people who've become homeless from coming out about their sexuality (and this is 2 people in real LIFE not online). So based on this, it's understandable that some of these people would feel a bit reserved about talking about their sexuality with heterosexual people, because in their life when they HAVE done that, it's become a huge problem. The reason these people probably feel more comfortable with LGBT people is they can relate with these hardships to other LGBT people. Even if you aren't homophobic I hope you can understand why these people may feel the place is "unsafe" in a way with non-LGBT people around. That's why some LGBT groups are exclusively LGBT. Obviously, heterosexuals do not have the same experience as this so don't really have the same reason to make a heterosexual-exclusive club.
Gay-bragging: I believe what a lot of people consider "gay people being in their face" isn't really so, but rather there is a bias to look out for things that one is not used to and ignore things that one is. You say that gay people brag about their sex lives, but I think straight people do that too, in fact I would say straight people probably do it, on average, more than gay people. Straight people check out women all the time, talk about their experiences and even show pornographic material to their friends or not (DISCLAIMER: Obviously I don't mean all straight people, but a large subsection of them do!), it's not something that's exclusive to gay people however with gay people it's a lot more noticeable because it's not considered the norm and we notice abnormal things much more than normal things. I'll give you a personal example of this, I went to the opera house with my boyfriend and I kissed him for a picture shoot, we got a LOT of stares, I was ok with this but I was noticing that everyone was staring at us. I'm sure a few people were posting on social media and what-not "More gays just pushing their gayness in public" and what-not, meanwhile two other straight couples had done the same thing, with no where near as many stares. People just notice abnormal things more I think.
It's funny cause, this sort of goes to a post I saw. Now not saying you're homophobic in any regard but I'm just posting the exact quote (which uses the word homophobic). "Homophobia is the fear that men will treat men the way men treat women".
Now all this said, I'm not saying I entirely disagree with you. I'm not a person who is sensitive about my sexuality, a lot of the time people mistake me for being heterosexual or asexual cause I'm very lax about it. I'm not an activist, I don't get offended if people say fag or whatnot, I'm completely fine with being treated like anyone else. But this post wasn't for me, it was for other people that I know AREN'T fine with that and have, I feel, legitimate reasons to not be fine with this stuff.