To me, the purpose of quotas or affirmative action is to undo a previous distortion.
In my experience, if you look at young kids, no matter the gender, ethnicity or class, they are all equally interested in science. But as they grow older, they start to move apart. Many boys who want to study but don't know what choose physics or computer science as a "default" (like I did). Girls are more likely to default to humanities or a teaching career. The really passionate kids are less affected by this, and choose what they want, but I know a bunch of people who chose the supposed "safe default" and were miserable or dropped out. It is not just bad for them, but also for society, if we are training some additional mediocre men, and missing some talented women in a field.
Same applies to other categories. When I look at my kid's classmates, you can tell unfortunately who's parents have the time and money and energy (and habit from their own upbringing) to support them properly in school, to read to them, and so on. The difference is minimal in Kindergarten, but kids drift apart quickly.
What I'm trying to say is there is a funnel in life. People who are not as priviliged as maybe I am, often "play in hard mode". To me, quotas etc. are not exactly about achiving justice or fairness or equality (you could do that by disadvantaging the priviliged, so that everybody is equally bad off. I think that is what many people fear when they think of affirmative action!). It is about righting a systematic wrong.
And it is not like AA means we will be giving stupid people scholarships. Right now we are often accidentially prefering less qualified people just because they are white or men. Trying to steer against that can only be a net win for society.