"Why do transwomen get so uptight about natal women getting together to talk about issues that only impact biological women?"
I've had a look at kiwifarms (it can be viewed without an account). It's clearly made up of both male and female members, and the threads aren't what I would describe "women's issues". It's just thread after thread about transwomen, the members falsely accusing them of rape without evidence, stalking them, violent threats and hateful slurs.
Someone asked if I had reported any illegal activity to the police, yes of course. Mumsnet don't seem to like the specifics being posted on here but I have witnessed and reported violent threats.
You aren't kidding anyone but yourself when you say kiwifarms is "just to innocently laugh at transpeople" or claim it's a "women rights site". From what I've read about Ovarit it seems to basically be the same thing but without the violent threats or suicide-goading.
It's certainly ironic these are the same people who get upset by an ancient Roman Latin prefix...