I can only really come at this as a fictionkin guy who awakened via tumblr in 2016, but
I really wonder if the emphasis on involuntary alterhuman identities (and subsequently dismissing/downplaying voluntary identities) wouldn't be as strong as it is if not for the ye olde kintype-policing and harassment dramas of the mid-10s
Granted, there's definitely a variety of factors going into like. trying to appeal to the mainstream by arguing "but we didn't choose to be this way!", but it probably feels like even more of a pressing matter to stress that when assholes are breathing down your neck and calling you a piece of shit for kinning the wrong characters in the wrong way (and outright disbelieving that kintypes can be involuntary at all, and dismissing that as just a lousy excuse to justify having problematique kintypes)
the fundamental problem here being, of course, the refusal to respect differences in experiences and beliefs. and being assholes.