UH OH SOMEBODY CALLED THE BIG EDGY GUYS! WHAT DO I DO!!!!!!
For those of us who are actually capable, let's think for one little fucking minute here. Why do we divide people into genders via pronouns? Because there are semi-exclusive commonalities between them which are important enough to every day life that it's been convenient to convey that distinction in reference to them. How someone thinks of themself, how they act, and how they try to appear with regards to femininity/masculinity are included in that regular daily social interaction. Chromosomes and even sex organs are NOT part of that.
To call a trans girl a 'she' is not to claim that their DNA has magically shifted into that of a genetic female. It simply makes the distinction that between projecting a feminine or masculine persona to the world, which is all that concerns anyone in day to day life, theirs is feminine. To NOT accept this, to stubbornly insist loudly and pointlessly, whenever you can, that the completely made-up social construct of gender as opposed to genetic sex is sacredly immutable is to say DUHHH YOU CAN'T BE A GIRL. I WON'T LET YOU. IT'S ICKY. IT'S SCARY. THE NEXT GENERATIONS WILL SWEEP ME UNDER THE FUCKING RUG FOR WHAT A DUMB PIECE OF SHIT I AM. That's all you accomplish, so great job. I'm a man and I've always been content to stay that way, but I can also choose not to be a pointless neanderthal.
And by the way, yeah tumblr and their crowd are fucking stupid. Much, if not most of what they say and fight for about 'social justice' is fucking stupid, but if tumblr was around during the fucking american civil war, during the women's rights movement when they couldn't fucking vote yet, during any other time in human history in which a class of people has been treated ignorantly and barbarously, you can bet that idiot pieces of shit the world over would have been writing off progress by conflating it with that opposite extreme just like you're trying to do.