I'm a genetic realist in this sense, you're either XX or XY and if you aren't, well, bad luck for you but you're a freak.
That said, I have no problem at all irl treating people as whatever gender they present as. I may not actually believe you're a woman, in the traditional sense, but unless I want to fuck you, why do I care?
For instance, suppose you're a guy I work with, and you really love your kids, and insist on showing people pictures of them. He thinks those kids are really great and wonderful and smart and whatever. I don't agree. I think they look like fucking downies and they're ugly as sin and I'd probably kick them if I saw them crawling out a sewer grate. Do I tell this guy at work that I think this? No.
I also don't tell that tranny that he looks fucking ridiculous.
It's a little thing called courtesy.