because, apparently, it's not enough to be an actor - you should have the lives experience of the character you are playing
Goodness, I'm quiet amazed that they ever managed to cast horror films. Imagine having to find enough actors with sufficient lived experience of being a zombie, or vampire, or superhero...
I wonder how those auditions go? 
In all seriousness though, like so many pps, I struggle to find much sympathy for him. I'll save it for people on the receiving end of death and rape threats for daring to speak about biology. It was only a matter of time before the purity spiral backlash reached him. The problem is I think we're more likely to see an apology for it (perhaps with a mild justification that he was trying to raise awareness and be an ally, but realises now that it wasn't the right thing to do) than the sudden realisation that the extreme left have gone so far around they're just popping back up on the right and just maybe JKR deserves an apology.