Affirmative action wasn't necessary to open the medical, legal, etc fields to women in the 80s and 90s (in the USA) and those fields were far more misogynistic than STEM is today. Moreover, I don't see much of a difference between your professors who say "girls are probably cheating" versus our wider society who contend that "boys are only successful because of privilege". Both seem wrong. Further, it's not clear to me that affirmative action is known to be successful. I've read several reports recently that indicate that corporate DEI initiatives (which I think is roughly revamped affirmative action) may increase discrimination because people believe that minorities are benefiting from their identity rather than their qualifications. Lastly, it's not clear to me that we need exactly 50% of a given field to be female--it seems like we need enough representation to ward off sexism and so on, which shouldn't require very much considering men don't act as a class (they don't advocate for "men's rights" and so on).
