Look up intersex people and marvel at how loose the definition of being female is. People are born without a womb, mixed genitalia, any combination you can imagine. They’re still considered women. If one can get to such a state, or further, they should too.
Look up the various studies performed on transgender patients showing how their brain is more aligned to that of females (or males, whichever way they swing), at a biological level.
Look up how hormonal imbalances during pregnancy can cause such discrepancies. It’s not just a psychological thing, it’s a biological phenomenon that does appear in nature.
Or don’t. You’re free to remain ignorant, just like you’re free to say whatever you like, but don’t act like the victim when you knowingly say something that’s considered out of line and face consequences.
Facing consequences for your actions is nothing new, don’t act like it is. Work places and public spaces have had rules of conduct since the dawn of time; what is considered acceptable has shifted as society evolved. You may not like it, but that’s not going to change just because calling someone by their chosen name makes you uncomfortable. Would you consider being disallowed to call black people slurs totalitarianism?
You are free to say whatever you want, just like people and employers are free to not want to associate with you for the things you say.