also the "queer stuff is ok because it's natural and we don't have a choice" is fallacious thinking. some serial killers probably don't have a choice in theirnature but that doesn't make murder acceptable.

But gender is a social construct, so how is it possible that a newborn infant who has had no exposure to society already has a particular social construct that they identify

the social constructs of gender might be a labelling system for a mental component of what we categorize as biological sex; that would exist in humans who were raised by wolves or aliens or whatever and didn't receive the signs and signifiers. Some nonbinary genders are very old in some cultures but some of the ideas for specific subsets of nonbinary are of recent coinage and there are surely long-dead humans who would've identified with xenogenders or any yet-to-be-delineated terminology if only they had the words to describe themselves at the time. like how there were always ace people even though societies didn't necessarily recognize them on the same footing as the allo orientations.