It's a deeply corrupt sort of nonsense promoted by people who want special treatment & to force others to participate in their delusion.
They believe they can change reality by bullying & manipulating people around them into using different words.
I think there are a number of things driving this all at the same time. A lot of people eat like crap & consume a ton of hormone disruptors that actually cause them to feel screwed up. Bad food also makes people foggy headed & unable to think straight. A lot of people are also lost & feel that life is meaningless because they are so disconnected from how everything works (most can't even fix their own toilet, much less a car or produce their own food, & they probably grew up surrounded by dysfunctional relationships). If you don't know how anything works, then you don't know why things are the way they are, so it's easy to decide things are evil & then try to manifest some sort of meaning into your life by trying to change them. And then, on top of their hormone disrupted, foggy headed ignorance, you get the prioritization of social status over the pursuit of knowledge & understanding.
Many who prioritize social status (and power) above other things both consciously & unconsciously want to destroy or undermine & enslave the people around them. A major step in enslaving people is to demoralize them & get them disconnected from reality. The idea that men can be women, & women can be men (or anything outside of that) is just a biological version of Orwell's 2+2=5. Once you destroy something as fundamental as the knowledge of what a person is you can get people to believe any sort of nonsense that serves you at any time. "Truth" becomes something that comes only from "experts" & "authorities," & it changes based on the situation.
The "they/them" people are tangled in a sophisticated manipulation & are also participating in it to elevate their own sense of social status without any merit what so ever. Many of these are the same losers who attacked people for not wearing masks or avoiding the jabs. They fall for every propaganda campaign & have probably recently said things like "Stand with Ukraine" or "Trust the science" even when those things were actually promoting WW3 or some sort of irrational athoritarian insanity (respectively).
"They/them" is a good indication that you are dealing with someone who is very confused & untrustworthy.
