Because he can't face up to the fact that a man who pretends to be a woman is not entitled to demand access to spaces and events reserved exclusively for women.
How are you going to stop them?
We know why you want to stop them, it's to make women's rights higher than another group's rights. But you refuse to recognise that the other group exists. So you're trying to improve women's rights over an imaginary group. Unless you accept that that group exists.

So your argument is self defeating.
You also want to stop something which doesn't currently happen, sex abuse of ciswomen by transwomen in single sex areas.
But you refuse to accept that transwomen exist, so how can ciswomen be sexually abused by those that, in your mind, don't exist.
So your complete belief and argument is based on either something that you don't believe exists, i.e. transwomen, or genuinely doesn't exist, i.e. sexual abuse of ciswomen in single sex spaces.
I'd say that your TERFism belief is based on an irrational fear of nothing, or an irrational fear of something you don't believe exists.
And the nearest you can get to a discussion is childish ad hominem arguments, strawman arguments and meaningless slogans.