I see what you're saying Confusedpleaseeducateme but if you break down what you are suggesting - men who ID as women AND who've had surgery are OK to use the women's toilet - you come up against some problems:
First of all, even post surgery, they are still male. So if the law says only females should use the women's toilets, that means that male genitalia or no male genitalia, they are not allowed use the women's toilet.
Secondly, it's frequently asserted on here - sorry I don't have any proper reference - that most transwomen do not have surgery, so they have their male genitals, and therefore, by your logic, have to use the men's toilet.
Thirdly, can you imagine having to sort out which of the transwomen still had their male genitalia, and which of them hadn't, and therefore, according to you, should be allowed into the women's toilets?
It's all waaaaay to complicated!
Current toilet arrangements are OK for the vast majority of the population.
The tried-and-tested arrangement of men's, women's [defined by biology] and disabled toilets has worked well for ages, there's no real need to mess with it just to placate a tiny tiny percentage of the population.