I'm talking about Trans females with their penis hanging out and want to be accepted among females and trans females at a spa or what have you. They can go find their own place to 'hang out' at. Don't like it, I don't care.

I can tell you don't care. But you can certainly see why they care that you have that attitude - and why many normal people disagree with you.

A majority telling a disfavored minority that they should go find their own place to hang out, rather than being allowed in the places where other people are allowed to hang out, has a long history in this country - and it's not a very pleasant or admirable one. We've had centuries of majorities telling members of racial, national, and religious minorities that they don't deserve to be accepted in established places ("No blacks, no Irish, no Jews"). Ironically, women too were often excluded from many places they wanted to be, and castigated for wanting to be accepted in male spaces (like country clubs or corporate boardrooms) instead of finding their own place to "hang out" at.

Why can't they just leave men alone? Why can't they just leave white people alone? Why can't they just leave Protestants alone? Why is it that all these women, blacks, and Catholics insist that they should be allowed to participate in the same spaces as other people, instead of having the decency to confine themselves to other places?

I mean, you asked the question. It's your thread title. "They" (which in this case would include the state legislature, and not just trans women) aren't leaving "women" alone for the same reason that "they" didn't let prior majority groups use discrimination to exclude minorities they didn't want to have around - to support the dignity and humanity of the minority group. To grant them the right to participate on equal footing with other people, even other people that might be uncomfortable with the idea of having to interact with the disfavored minority.