I for the most part agree that gender and gender roles are a social construct but sex, nah. Sex is biological, it's concrete science. Gender on the other hand are a set of societal and cultural pressures exerted on people based upon their biological sex.
well how to you explain the variance in sexual characteristics?
and are you ready to marginalise all the people who do not fit comfortably into "male" and "female"?
I don't know how one does "not fit comfortably into male or female". You either have a penis, or a vagina, and that is literally just that. It's what determines your sex. if you do not believe that, then you need some psychological help. Now, how you want to use those said tools, is entirely up to you, and completely okay (Unless harmful to others).
Like who cares if you're a very feminine soyboy, or a dude with actual tits, if you got a penis, you're a dude, nothing else. It's not complicated. If you are a dude, who thinks of yourself as a chick, and force other people to succumb to your own irrational views, you're a psychopath.