You're assuming that what we've been doing DOESN'T result in some mental harm just because it's the norm.

If it doesn't, then why are so many suffering needlessly due to gender tropes, stereotypes, and pressures?

Deciding to raise children without gender is a response to a lot of gendered nonsense that has gone to extremes wnd has become dogmatic and harmful to many.

We don't know it's better. We don't know it's worse either. Time will tell.