I'm assuming that Alice believes that race is a social construct with no underlying biological reality and would like this construct to go away -- the ideal is an entirely colour-blind world.

That seems to me to be assuming more than is actually called for here, but never mind.

Given that racial discrimination is bad, Alice would want to get rid of all forms of it, including affirmative action.

If that means that Alice's ideal world would have no racial discrimination anywhere ever (and, in particular, no affirmative action) then yes, I agree, she would. If it means that given any hypothetical world she would consider removing affirmative action from it an improvement then no, I don't see any reason why that should be her position.

What makes affirmative action special? The fact that the full force of the state is behind it.

Affirmative action generally takes the form of preferential hiring or enrollment practices by employers and educators. It has "the full force of the state" behind it only in that it's generally government departments and state-run universities that do it. It's not like you're going to have the US military mounting a shock-and-awe campaign against your house if you speak out against it.

It seems to me that there are other things that distinguish affirmative action from most other forms of racial discrimination.

• It is generally limited in ways that they aren't. That is: if I am a conventional racist running a company, I will simply never hire any black people. If I am in the same position and doing affirmative action, I probably have a quota: I will try to make 20% of my hires black people, or something like that.
• It is explicitly aimed at adjusting for wrongs done elsewhere. The goal is not, so to speak, to maximize local justice, to do what you would consider the Right Thing if you look only at the immediate situation; it is to improve things overall, balancing unfairness in one place against opposite unfairness in another.
  • For the avoidance of doubt, I am not claiming that this is a good idea nor that it is done well. Only that that's the intention, so that "look, you're being locally unfair" is a pointless criticism: the Affirmative Actor knows that, and if you want to convince them you need to persuade them either that the local unfairness is not successfully counterbalancing opposite unfairnesses elsewhere, or that the whole idea of balancing such things out is ill-conceived.
• Its intended beneficiaries are, as a group, worse off in many ways than its intended victims.

Do these really make a difference? Good question. But you can't possibly argue in good faith against affirmative action while pretending they aren't there, which is what you seem to be doing so far.

I don't hold that position

OK. It looked to me as if some position along those lines was the most likely justification for the inference you seemed to want to foist on Usul.

if race [...] is an arbitrary label, [...] I'm not sure what makes it special.

In regard to affirmative action? What makes it special is the fact that people have been discriminating on the basis of race for years and years, and often still do.

For the avoidance of doubt, I am not myself claiming that race is an arbitrary label; I'm not sure Usul would either, but you'd have to ask him. But even if it were the fact of past and present discrimination on the basis of that arbitrary label would be a sufficient explanation (though not necessarily a justification) of the existence of affirmative action.

at this point in time you do not fix past racial discrimination [...] by institutionalising a reverse form of racism.

It's too late to fix anything that happened in the past. It might not be too late to fix some of its residual effects. And it's not as if racism (of the usual anti-black sort) stopped when the "Civil Rights era" began. The stuff affirmative action advocates hope to counterbalance isn't all decades ago -- some of it is still happening now.

It is clearly true that if there is a path to a world where race simply doesn't matter, then it needs to end up with race simply not mattering, and that will mean no affirmative action. But that doesn't mean that the best available path to such a world begins with ending affirmative action.

(Again, for the avoidance of doubt, I am not claiming that in fact there is any way to get such a world, nor that it would be a good world if we did. The question is: if someone wants a colour-blind world but doesn't agree that we should start by ending affirmative action, does that indicate hypocrisy?)