In a perfect world, affirmative action would be completely unnecessary, although people might still use diversity as a consideration in hiring practices because sometimes diversity can help people with aspects of their jobs that aren't explicitly tested in the job qualifications. For example, when hiring a teacher, presumable the main job qualifications are knowledge of the subject matter and teaching ability, but teachers can often also act as role models, and having a diverse set of role models can be preferable to having a homogeneous set of role models.
However, we don't live in a perfect society, and until we do, affirmative action can help remedy some of the inequities that result from negative discrimination. There are certainly some inequities that are remedied by affirmative action, and some other inequities that are caused by it, and some other inequities are caused by the very idea of it (both by giving people the idea that they need handouts and by making them wonder if they deserved a job when they really did.) To me, the question of whether affirmative action is a good thing depends not on theoretical considerations, but on practical measurements of how the inequities ameliorated compare to the inequities caused, and so it is really an economics problem, and I'm sure I don't know if there have been any studies done to compare the economic and social costs to the benefits of affirmative action, which is what it would take to convince me whether it was a good or a bad thing in today's society.
As far as what dysfunction said about our efforts being better spent solving the underlying problems, I completely agree that it is worthy of our effort, but one of the advantages of affirmative action is that it really takes very little effort to enact, so it's not like it takes away from our ability to make more long term proactive changes. I think it should only be abandoned when it seems that the disadvantages are as great as the advantages. (It's possible that we may have crossed that line already; I'm not taking a position on that issue since I don't have enough data to make a sound judgment either way.)