I think the debate regarding affirmative action is very simple and not unexpected at all. Here's how I view it.
To start, in America I believe that most of us believe that the "default" behavior should be to avoid unfair discrimination, especially for protected classes. I think most people would agree to at least this, it's a pretty generic and obvious statement.
Therefore, when we deviate from this for some reason, generally, it REQUIRES a healthy amount of thought: the baseline should be at least a strong hypothesis to begin the conversation. The world is very complicated, so simply assuming something does what you expect it to because it intuitively sounds like it does is generally not a reasonable position.
And of course, the idea behind affirmative action, hopefully put into words that people feel is fair, is a sort of discrimination, but the intention is of course to try to adjust for past disgressions and injustice to try to "re-balance" opportunity. So unlike the four-letter-word that was discrimination in historical contexts, it is not based on racism[1], for example.
So does affirmative action work? It seems to do roughly what it is supposed to do, although honestly a huge problem is that it's sort of tautological. Of course it works, at doing what it's meant to do. Some have argued that it could potentially harm students by leading to a "mismatch", but the evidence is mixed and in any case it probably causes more good than harm in terms of outcomes. I am not an expert on this though, and I have not been into the studies for a while.
The real question that I think causes so much strife and pain is the one that hurts to try to answer: is it worth it? And that is not easy to answer, nor does it have an obvious objective answer. I truly believe that most of this argument boils down to proxies for this particular question. Some people who have a particular egalitarian bend to their views on life and society might blanket oppose such a policy on an ideological basis, whereas someone who is strongly anti-racist is highly likely to prefer such policies even at high cost.
Cost? By that, in this case I mean in terms of going against the basic belief of not discriminating. Ideology is important to people even when there isn't a discrete cost, but in this case the micro and macro views are very different. On the micro level, someone who is less qualified will be preferred over someone who is more qualified, on the basis of factors outside of their control. On the macro level, population demographics change, generally reducing biases.
There's a lot of finer points. Like clearly, on the micro level, when someone "less qualified" according to some criteria passes due to affirmative action, the idea is that it was beyond their control in the first place that they were less qualified, which may very well be true. And on the macro level, statistics may not tell the full story: demographics are a measurement of people, and people are not fungible. The numbers surely look better on paper, but one must wonder sometimes if it's actually doing what it looks like it's doing.
You might think that I am staunchly opposed to affirmative action based on my framing of this, and the truth is, I simply don't know. I think that it's potentially very powerful, but it also is damn scary to wield institutional discrimination even if it's supposed to be a force for good. This isn't exactly a slippery slope situation, of course, but the road to hell is paved with good intentions. I've personally flip-flopped probably a lot of times. All I can say is that I sort of hope people don't just assume this is the right way to solve all of the problem of injustices, or maybe even more importantly, that merely instituting policies like this doesn't "solve" America's history with racism and sexism; and I don't think most people believe that it does. For some of those things, I think only a lot of time will truly be able to heal most of that, and it's going to leave a pretty nasty scar.
Of course, beyond the fairly straightforward debate is the culture war bullshit surrounding it, but to me it's mostly noise. I look forward to a future with less influence from Twitter and news organizations so that people can go back to discussing things at least slightly more like human beings.
[1]: Using racism in this context to refer to the fairly strict definition of being related to beliefs about races rather than about discrimination.