Biological sex, and the need to detect and act based on it, goes back to single celled organisms. It predates complex life itself. It’s that fundamental, and understanding it (in some sense) and acting on it is histocially necessary for everything that has happened since that point. So confusing it, tearing it down, eradicating those fundamental categories, is deeply upsetting and anti-human, because it undermines one of the deepest and most necessary ways in which humans (and in fact almost all complex life) understand the world and themselves and determine how to act and find their place in the continuity of biological life and our species history.

That’s upsetting. It’s not a minor change to the territory of the mind. It is a deconstruction of the most fundamental basis of our biological and psychological and conceptual structure. That’s a big loss. You can’t suffer it and not feel pain. It’s a rejection of the fundamental structure of life and multiple layers of human identity. You can’t take apart something that has taken hundreds of millions of years to establish and refine and has cost an untold number of lives across all species and levels of complexity and is the basis of everything that’s been built since just after the development of internal cellular specificity and say “No, that’s not a thing, it’s whatever we want it to be; figure it out for yourself,” and think you can just figure it all out in a stable and coherent and successful way all on your own in a couple years.

There have been hundreds of millions of years and untold billions of lives lived and lost put into getting us to where we are. You aren’t going to be able to just tear all that down and replace it in a few years on your own (or even as a society) just because you think there’s a chance that you might have come with something better. That’s like blowing up the Earth on the off chance that living in space might turn out to be better, and people will just need to evolve and adapt to conditions there individually in the time they have once the bombs go off.
Sure, people have maybe been too reductive and rigid about gender, and we do need to be balanced and adaptive and wise as conditions change, but that rigidity and emphasis happens just because gender and sex really are that important to fundamental human identity and function and action and survival. It’s the sort of thing that if you lose your understanding of it, and if you lose the ability to act coherently and effectively based on it, you’ve lost something enormous. Something you can’t afford to lose. And so people put up protections around it, because it’s not the sort of thing you can lose or dissolve and survive.