how do you propose stopping males using womens spaces? There is no way to do that today, if the world is how you want it we need a mechanism. What would that be?
I never understand this argument.
The mechanisms to stop domestic violence and rape, for example, are very weak. Probably far weaker than those to stop males appropriating female toilets. But we still have laws against rape and DV. No one would ever say "we don't have a mechanism to stop rape or DV so we'll just have to make them legal".
Laws aren't magic, they don't stop the thing that is illegal ever happening, they just allow prosecution after the event. The idea is that most people, knowing it's illegal, then don't do it. Some out of fear of prosecution, but most simply because laws send a strong message about what society does and does not condone, and most people, humans being social creatures, will fit in to society.