Maddy, there are nice, lovely, respectful men who aren't trans as well, who wouldn't hurt a fly. I'm sure we could find some evidence or facts about them if we try. That doesn't mean they can go in the women's toilet, changing room, hospital ward or prison cell, or sports.
These are things for women, where they can be safe, not just from actual harm, but from fear, worry, the discomfort of being watched or heard by a male. Why do you think they exist? Because women need that safety and privacy from men. A man claiming to be a woman is not just a man, he's a man pretending he knows what's like to be a woman when he actually has no clue - he hasn't lived that reality – and thinks his desire to be in their space matters more than their feelings. That makes him disrespectful, sexist and misogynist and proves he can't relate to women at all.
You know that some women, for religious reasons, reasons of past abuse etc now just self-exclude from these spaces because they can't trust them to be female-only now? They just don't go. If they have to do that, your friend and his ilk could do that instead and give them back what's theirs. That would be fair. In fact he's just doing what so many men do - putting himself and his wants before women.