I am always surprised when well educated people misunderstand or misrepresent opposing arguments, or reuse data points that seem to support their side as some sort of argument-winning trump card.
> claiming that sex is not something inborn
Literally no serious[1] person studying gender makes that claim. The reason it's hard to understand is because the actual argument has always ben that both nature and nurture play important roles. As for why "culture" applies, remember that while sex involves genetics (and hormones, etc), gender is performative. Performance happens in a setting, thus acting masculine hap[ens in a culture/setting that defines what "masculine" means.
> Clearly man and woman are different physically
Obviously true in general, but there are surprises in the details.
> and mentally
That is technically true, but presupposing that is bad science. Historically a lot of stupid crap was invented to justify the two predefined[2] categories. More importantly, anybody claiming there is a difference needs to explain the specifics of which traits they are talking about, because for most attributes the bell curves overlap significantly.
> Lysenkoism
If you want to be paranoid, you will find ways to interpret your experience as being persecuted. Instead, I suggest actually listening to the actual arguments being made.
[1] I'm sure you can find examples of almost any claim in forum comments.
[2] Science should create categories from the observations. If you're starting with the two categories [M, F] and then trying to prove or disprove that, you're doing it wrong. These concepts are more complicated than a simple Boolean flag.