Online I use "they" or *them" quite often when talking about people whose username doesn't reveal their gender (and quite frankly this is the default).

So I am not sure why people have negative feelings about people unwilling to communicate themselves as member of one gender for one reason or another. If someone feels that way, they very likely have a metric ton of friction with their surroundings anyways — which is in itself certainly quite unenjoyable and certainly not something people tend to desire without a huge internal urge. Calling them "them" doesn't cost a lot (especially considering that we do this with strangers on the internet already) — why not just do it?

I know people that have the general assumption that people want to be called by another pronoun for neferious reasons like a implied urge to "get attention". But I think this is not only a oversimplification, but also a statement that rarely describes the reality of the person they talk about if you do the research a d actually get to know them and their reasoning.