How do Democrats still not understand that giving concessions to the "merits" of fascist rhetoric (like they're doing with trans people as well) will never make people think you're more "reasonable", and will always further normalize hatred?

Because they agree with the fascists. The only thing they don't agree with is the rhetoric. They hate the aesthetics of the right, but they want the same things. Libs just feel guilty about it. Libs affectations and rhetoric is only about assuaging their guilt.