Affirmative action does not eliminate discrimination, it enforces discrimination up to an arbitrarily defined standard.
Suppose you're applying to a company that's posted 10 openings and has already filled 7 of them, and that you belong to category A, and there's three more candidates who belong to category B. Suppose further that it can be objectively determined that you're a better fit for any of the openings than any of the other candidates, but the company has already filled its category A quota. You will be rejected because of your category, and the less capable candidates will be accepted also because of their category.
Note that it doesn't matter how the categories are defined in my example. Maybe you belong to a privileged (in the social justice sense) class, but it's equally possible that you belong to a disadvantaged class and the inept candidates belong to a privileged class.
Suppose you're applying to a company that's posted 10 openings and has already filled 7 of them, and that you belong to category A, and there's three more candidates who belong to category B. Suppose further that it can be objectively determined that you're a better fit for any of the openings than any of the other candidates, but the company has already filled its category A quota. You will be rejected because of your category, and the less capable candidates will be accepted also because of their category.
Note that it doesn't matter how the categories are defined in my example. Maybe you belong to a privileged (in the social justice sense) class, but it's equally possible that you belong to a disadvantaged class and the inept candidates belong to a privileged class.