Let's just be clear on where the status quo is. Eugine_Nier has mentioned disparate impact analysis several times. In addition to that is the far more important disparate treatment prohibition.

In the US, a worker can get fired even if it is not for cause. If you boss thinks you are a terrible worker, you can be fired even if you could prove your boss is wrong and you actually are a great worker. But you boss would be liable for wrongful termination if the boss said "I think [blacks / whites / Germans / Russians] are likely to be bad at your job, and you are [black / white / German / Russian], so you're fired." Likewise, an employer can't refuse to hire on that basis.

Proving that is a separate issue, but having no public policy based on race implies repeal of both disparate impact prohibitions and disparate treatment prohibitions (and lots of other stuff, but it's complicated).

Accurate beliefs about what? If a group (however defined) has been subject to negative discrimination, however arbitrary, then there is an argument for treating them to a period of positive discrimination to compensate. That has nothing to do with how jusitfied the original negative discrimination was.

And why do I need to be told "that there exist genetic differences between races that give rise to behavioral difference". I have said nothing about affirmative action/positive discrimination one way or the other. You raised that issue. But you didn't say how they two relate.

I'm not sure whether the cause is genetic or cultural but there are most definitely behavioral differences between the races. Furthermore, the fact that it's politically impossible to talk about this is causing a lot of problems. Consider the state of US cities with large black populations as discussed in this blog post by Walter Mead. The behavior in question is probably purely cultural since historic "white ethnic" political machines lead to the same problems, on the other hand the fact that this political machine is black means most people would rather pretend the problem doesn't exist than talk about it and risk getting called "racist".

For another example, consider the campaign to force Rhodesia to accept majority rule. Given the subsequent history of Zimbabwe this campaign almost certainly resulted in a worse situation for everyone involved.

And are they?

No, that's the problem.

By the way affirmative action is by no means the only race-based policy, just the one simplest to describe.