I'm trying to point out, that things aren't as clear cut as they once were, we can't look and assume that we know someone's sex. We can't test for sex in loos and, even if we could, it's no guarantee of being safe.
So because some very convincing Trans women manage it now, we should just say - "Oh, we can't stop everyone, it will be OK!" How is that even an argument - you can't remove all risk so why bother at all?
If I walk in the changing rooms in my sports centre, and there is a man stripping off in there, I can get security, and he will be removed. I doubt it would matter how good his make-up was/wasn't - he would be removed.
Under the the proposed changes, he only needs to say, "But I am a woman, I feel I am!" , and he will be allowed to stay.
Maybe you don't have any problems with this scenario, but many people do.