TBH though I think the thing @decepticonsensual was talking about regarding different outlooks having different starting points explains exclusion vs inclusion (if we leave out obvious assholes on both sides.)
If you value exclusion, you likely have experience with specific ostracism. For example, you are older and from a conservative place, and just plain being gay got you beat up. Or the gay group didn’t accept you because you are trans. Or you got beaten for being an autistic nerdy boy who loved video games before it was cool.
You’re likely someone who found solace in exclusive groups. You found other people like you, quite possibly who met in secret or hid from larger society. You developed your own cultural norms in parallel or in defiance of the larger community. You feel relieved when someone follows these norms because they aren’t a threat.
You quite possibly feel threatened and suspicious when someone who doesn’t know or follow these norms demands entry (and doesn’t act like a curious but deferential newbie who wants to learn), as if your bullies had tracked you down again. You will do anything to keep them from sneaking in and trashing the place.
If you value inclusion, you’ve likely ALSO been ostracized. But it’s quite possibly less specific. People know you don’t fit, but they’re not totally sure why. MAybe they label and attack you anyway. But maybe they do something a little different: what the fuck are you supposed to be? Maybe you seem totally abnormal to them, off the chart. (“Only a pervert obsessed with childhood would dress in a fur suit.”) Or maybe you are too close to normal for their liking. (“Wait, you married a man but you don’t fuck him? I’d get it if you were gay, but that’s just broken.”)
You’re likely someone who is not seeking out a group of people that is very similar to you, precisely because you probably think nobody is. You’re weird, is all you know, weird and unsafe and having to hide. So you go looking for groups of “weird people,” like the things people called you when they bullied you that weren’t quite accurate, but were a way to say Other, Bad, Get Out.
When you go looking for groups to feel safer in, you quite possibly feel devastated and hopeless when you find exclusive groups that don’t want to let you in. Whether or not the group’s explanation for being specific is genuine or valid, you’re likely to worry it’s just an excuse. But people making excuses to hurt you are bad, so you’re going to keep yelling until people let you in… whether or not they like it.
I see the appeal of this model, but as an empirical matter I suspect it’s wrong much of the time. At the very least – I personally come from a background of “weird non-cultural-standard group where exclusivity vs. inclusivity fights were a big deal,” and this is not even slightly how things broke down. Other groups I’ve seen have been pretty similar.
(Obviously I’m just arguing from experience here, and everyone’s experience is different, so…take with as much salt as you deem appropriate.)
So…as far as I can tell, there are basically two cleavages here along which people divide with regard to this issue. One is the obvious, boring one: “What is your social position right now?” People who want into a thing, who are mad about being or feeling excluded, are more likely to turn to inclusionist logic and rhetoric. Once they become the insiders themselves, and they have to deal with the very real cultural difficulties posed by a lack of gatekeeping (rather than with the pain of being out in the cold), exclusivity starts to become more appealing.
The other cleavage, which is more about deep-seated personality differences and less about opportunistic hypocrisy, is more interesting to my mind. It boils down to: “How do you feel about being Weird? What does that mean to you?”
The exclusionists are pretty happy to be Weird, and it doesn’t bother them that the world sees them that way. Often they take a kind of perverse pride in their alien inaccessibility. Mostly they want to hang out with their favorite people, and otherwise to be left alone. (This can arise from “you and your favorite people are all Weird together because you share a single Big Distinctive Thing,” as per your model, but it definitely doesn’t have to. I’ve seen eclectic assemblages of misfits come together on this principle.) They tend to be either individualist or tribalist in outlook. They’re very happy to use exclusion as a shield, in pretty much the way you describe, but it’s noteworthy that they’re also not inclined to be bothered by the idea that other people are going to exclude them from things.
The inclusionists don’t think of themselves as Weird, except maybe in bitter defiance, and it bugs them that Weirdness has been thrust upon them. As they see it, there is something wrong with the world that excludes them, and they don’t want to replicate its evils. (Or possibly they’re more-socially-successful people who don’t see their
thing as being Weird at all, and resent the
we’re-not-part-of-the-mainstream thinking of the exclusionists.)
They tend to be rules-oriented* in outlook, and to think – at least implicitly – that you need an Official Satisfactory Reason to keep someone away.
* The “rules” in question can be anything from small-town religious conservative mores to social justice.