It's not illegal for a man to go into the Ladies, I'm sure.
I've seen men in there - when they've asked and women have said OK - to change babies when there's not a changing thing in the gents, of course boys including sometimes older boys are in there with their mums, and of course in the past old style TIMs who were a. trying to pass very hard and b. very few and far between.
It's illegal for them to go in there and then do something illegal obv.
The difficulty is twofold:
Previously, we could turn a blind eye but if someone was iffy, then you could challenge them, ask them to leave, go and get security if in a shopping centre etc. This "iffyness" could be on the right side of the law - hanging around, staring, approaching women and girls, talking to them, standing too close, all of the sort of stuff that creepy men do that is not illegal. Before, the fact it was a man meant that we had some power to get him to leave because by very well embedded social convention he was not supposed to be here. Now that is removed, and we can only act when they do something illegal, and there is a lot of stuff they can do before they break the law.
On Harvey Weinstein, I don't understand why it would be illegal for a man to ask a woman watch him shower, but not a woman. Where are you getting this stuff? Generally I don't think it's illegal for a person to ask you something, even if it is a creepy something. For an employer to do this to a subordinate might be (should be) an issue for the company to deal with if raised, but I don't think there's any difference on sex configuration, man/man, man/woman, woman/man, woman/woman, it's always creepy to ask someone (espeically somene much younger and better looking over whom you have power) to ask them to watch you shower.