I'll give it a shot.
Not only are "trans-women" truly women....they're the only women.
The only true women are biologically male who identify as women and only true men are biologically women who identify as men.
(I tried to give a rationale for it, but the more I tried to come up with a rationale, the more it started to sound like something a leftist would actually believe because I started invoking words like "Cisgender" and then realized just leaving that statement as is, is more sufficient and crazy sounding than explaining it)
I wish. I don't think there's any abhorrent premise you won't find some of them advocating for, and not just one or two individuals, but whole groups. Heck, "trans children" is mainstream. They write articles defending pedophilia. Some even say it's healthy.
There is nothing you won't find some subset of leftists defending and cheering.
It helps that they couch their abhorrent beliefs in socially acceptable terms. It's not eugenics, it's abortion! It's not illegal immigration, it's refugee migrants, etc....