I'm going to point out that I'm genuinely asking here, not doing the "I'm just asking questions bro" thing that so many XYZ-phobes do, just so people are aware I'm asking in good faith.
Why is demisexuality considered a sexuality akin to the whole LGBTQ+ grouping? It honestly comes across to me less like a sexuality and more like a preference, or just a sort of way your sexuality works as opposed to a sexuality in and as of itself.
I think it's important to know that it's there as a waypoint between "normal" and "asexual." It's sort of the point at which the accepted range flips over into the unaccepted range.
I'm speaking from the perspective of who I was as an uninformed teenager, but I ended up knowing about three asexual people as a kid and to me they all came off as "weird" in some indefinable way. One of them grew up to be AAA (agender, aromantic, and asexual), one grew up as a Very Cis biromantic Male who was willing to be penetrated if it would make his partner happy but couldn't do the other thing because he just straight up didn't care or want to, one is heteroromantic, trying out cross-dressing and thinking he might be demisexual after all.
For fairness and disclosure I semi-dated the last of these as a teenager; part of the shift from "ace" to "demi" may well have been the problem of being emotionally attached to someone who looks like a woman but doesn't act like one.
My first boyfriend was demisexual and wasn't at all frustrated or annoyed that it took about a year of dating for me to feel comfortable kissing him. We never had sex and that didn't piss him off either. How many straight men in their early twenties would carry out a two-year adult relationship and be all: "this is genuinely an ok way for this to be going" ?
The incel community alone shows a certain perspective on this point ...
At this point I think that the bigots have a point, which is that putting all of the 2S.L.G.B.T.Q.I.A.+ people together and saying "they're all one" does flatten a lot of complexity. But something we all have in common is as follows: cishet "gold star" attractions and ways of being are
very well defined. What we put under the queer umbrella are all of the things that make others draw back in confusion and disgust.
Demisexuality could be described as "someone who simply doesn't have sexual needs or interests outside of an established partnership and who is not prioritizing sex while they build that relationship, but where it will probably be important later." Because of church propaganda, this is usually treated as the norm for cisgender women, but I know based on my childhood as an outsider tacked into girls' and women's spaces that this is categorically not the way that most cis and het women are built.
This can be complicated for trans people specifically because of the way that we tend to be desired in ways that we don't want to be wanted, and people may want to do things with us that we don't want to do. But, at least from my limited perspective, I think it's easier for people to see the action of demisexuality in people's lives as you get older and see what the "normal pattern" is and then our friends and acquaintances who wind up taking another path.
Calling it queer without qualifications can be complicated just because we usually use queer as a shorthand for some variety of gay with a gender mixup on top, and demisexual is something you can be while both cisgender and heterosexual. It's very much like calling "intersex" queer when a lot of people who are intersex would not like to be called or seen as queer, thank you very much. But intersex people have experiences which are
very similar to trans people in many ways, so it makes sense to include them.
In that sense I don't think MOGAI (Marginalized Orientations, Gender Alignment, and Intersex) was a mistake. Are asexual people put to the margin? Yes. Often partly because people assume they are closeted queers, but absolutely, yes. They belong to what we often call the queer umbrella, but at this point I feel it becomes clear that, maybe, we shouldn't call all of this queer ... if you can be "gay but not queer," as many people are, or "queer but not gay," it's more precise not to use "queer" as the umbrella term.