But people don't just ... "decide" to be a woman. Yes, we need some sort of basic guardrails to keep unscrupulous scumbags from taking advantage of this, but no one just says "hey I'm a lady now".
Exactly. From the wailing on the Right, you would think this sort of thing happens all the time - so frequently that it serves the greater good to deny transgendered citizens equal access to government-run activities at public schools and universities. So where is it? Where's a single documented case of someone starting out life as one sex, winning any sort of accolade as the opposite sex, and then switching back?
What's that? You're saying that even though it hasn't happened yet, it *might* happen? That's your basis for allowing governmental discrimination? You might as well say that the government should ban all handguns because they *might* be used in crimes. Or that Conservatives shouldn't be allowed to vote, because they *might* vote for a treasonous puddle of orange drool.
Oh, wait. Strike that last one - not a valid example of an extreme hypothetical.