All very fascinating, but that’s *not* the current modern usage of the term. It’s an insult used to dismiss progressive opinions. Language changes; the term has been co-opted. It is not to be used in this community.
When I use the term, that's how I mean it. And as far as I'm concerned, you are flat out wrong in this: because in the circles I run in, that's where the term came from and was probably being used long before you even heard it used.
I concur it is often used as an insult, but not to dismiss progressive opinions per se. It's used to dismiss the insertion of political opinions into every aspect of every conversation, often when the way that the insertion is done is very ostentatious and in particular when what the thing the person is doing is not very costly, but the person doing it pretends that they are taking a great risk in presenting the opinion. When someone comes and says, "See how inclusive I am." as the very first part of a conversation, it's like that person with 21 bumper stickers on the back of the car. It may well be that inclusivity is a great thing, but you can still disagree that the person is actually displaying inclusivity, tolerance, and open minded behavior as they trumpet their own virtue and pet theorems.
For example, no one is going to get banned off of EnWorld for presenting a progressive opinion even when it is in violation of the terms of service. They know that, because they know that it is tolerated. You said it yourself:
"This community is unapologetically inclusive, and falls deliberately and firmly on that side of the line. I was hoping it sent more than "a bit" of a signal; I would hope that was blindingly obvious to anybody"
Oh, it is blindly obvious to anyone. What is really hilarious though is that you anoint that behavior as "inclusive", despite the fact that most of the time - indeed, pretty much all of the time - no one is trying to exclude anyone from gaming - except, apparently, yourself. Sure, you can tell yourself that you have valid reason to exclude people that strike you as jerks, and that's fine - maybe you are even right. But please don't validate that as inclusiveness. Labelling it "inclusive" though, poisons the well thoroughly, because it defacto declares disagreement with any part of the opinion is racist. Yet, no one ever gets banned or red modded on EnWorld for calling people racist in order to dismiss someone else's opinion. Or sexist. Or really, any of the left terms of dismissiveness which is blanket dropped whenever they are disagreed with.
As for the term in question, I often feel people find it the term offensive primarily because they resent the comparison.
Final note, so far as I can recall, I've not actually used the term on EnWorld to refer to anyone. I don't find it particularly useful even when I find the term accurate, mostly because people just get offended instead of reflecting on the fact that it's potentially very valid criticism, so it doesn't accomplish the purpose of changing the person's opinion. But it's not necessarily the opinions that bother people. It's the act of politicizing everything that I think annoys people. It's the equivalent of going around with a bible and a tract and knocking on people's door that annoys people. If you can suggest better language for, "I find your insertion of political opinions into everything you write more than a little bit annoying. And in fact, it strikes me as petty self-righteous passive aggressive behavior.", then by all means suggest. Because most of the description of the problem strikes me as a bit more inflammatory and biased that "virtue signaling".