Verbeena, I've read that thread though now.
I think part of the problem is just that very thing you hold to be true: "transwomen are women".
You say it's transphobic to even question this, so of course that thread is transphobic to you.
The problem is, at its heart that's a kindly meant social lie and not a fact.
I'm autistic, many of the posters on FWR are (or at least I've noticed quite a few saying they are). We're not good at social lies, these physically hurt us, and we're more stuck on logic than others.
We're used to not conforming with gender norms and we're used to looking for rules to make sense.
When does male actually become female? When does that become true, what's the switchover point? Is it surgery? Clothes? Special personality? Or a declaration? How do you tell if someone's dysphoric, taking the piss, or massively traumatised or autistic with other problems when just their declaration leads to medical intervention (according to transpeople on FWR)?
Is it ever really possible to switch biological sex on your say-so, and why does no other inner feeling suddenly count in law? Like age or race?
I agree that at the core of FWR is the premise that you cannot really change sex - though it doesn't mean that person no longer exists or that they don't deserve compassion and rights and love and so on.
Most of us used to accept and nod along despite the social lie, but then a massive internet movement has taken that illogical premise and bent it to the point of mass trollery.
The problem is, once you accept the social lie of male becoming truly female, with no distinction at all allowed, then how do you then legally look after females in law and keep some things for them (eg sports) and how do you protect women and transwomen from predatory males using the same vague unverifiable claim to enter female spaces? How do you protect "real" transpeople from actual hatred and attacks?
Sorry for the essay, I know it's not the point of this thread and I have to go to work, but it's hard to be told you're an unthinking evil bigot when it's all so illogical!