That's not how affirmative action works. Using your example, for most of the population, there is no detraction from their score. It only comes into effect if you have +1 and they have 0 or +1, and it becomes you with +1 and them with +2.
If you had +10 and they had 0, you would stay at +10 and they would go to +2, taking the place of someone else that only had +1 and leaving you alone. For you in this case it isn't a 0-sum because you never lose.
For the people on the edge, it is 0-sum because they are on the edge of not getting the position. Any advantage given to someone else removes them from contention.
Ah, I see. As I understand it, AA usually comes into play when there is little separating two candidates. Most other qualities are the same or the historically advantaged candidate is only slightly better than the disadvantaged one.
To counter this historical disadvantage, the candidate possessing it is given additional 'points' which push them beyond the other. All other things being equal or close to equal, this becomes the tie-breaker.
At what point does someone given these AA boosts at every step in their life (high school, SAT, college admission, job interview) no longer qualify to be called disadvantaged?
I got real into AA back in day, when I thought I was on the receiving end of reverse discrimination.
I learned that the biggest part of AA is actually just letting the kids know they qualify. We grow up with the narrative that after highschool you do college; and that you'll succeed at going somewhere. Not everyone gets that narrative, so a big part of AA is finding the kids that qualify for admission / scholarship / etc, and letting them know that. The next part is helping them apply; if no-one you know has ever navigated an academic bureaucracy, it's confusing and intimidating.
It's like the Black Panthers. Everyone knows about the least of their efforts (police watch), because it's also the most controversial. Few people know about the bulk of their efforts (school lunches) because it's not.
If you had +10 and they had 0, you would stay at +10 and they would go to +2, taking the place of someone else that only had +1 and leaving you alone. For you in this case it isn't a 0-sum because you never lose.
For the people on the edge, it is 0-sum because they are on the edge of not getting the position. Any advantage given to someone else removes them from contention.