Because it is just a prelude to acceptance of their sickness as being a way of life we should accept.
So what? How does that hurt you?
Just as many accepted homosexuality, some want to have sex with children, some want to legalize incest and beastiality.
FACT: the vast majority of pedophiles are heterosexual men. That's a real statistic and has always been the case. Most sexual molestations are perpetrated on a young girl by a heterosexual man. To equate homosexuality with pedophilia or incest or bestiality is absurd.
I agree that trans "women" shouldn't be allowed to use women's facilities or compete in women's sports. That opens up an enormous can of worms unnecessarily, especially since our overlords are either not terribly bright and can't come up with reasonable solutions, or they're causing societal friction on purpose.
But when it doesn't directly affect me, I don't give a damn what people do. Why do you?