I don't want to go in circles here because as I said I agree with the rule for the reasons you an eball stated but the rule is in place to increase the representation of minorities in the coaching ranks, which is a quota based goal. People don't feel that there is enough minority representation coaching. It's not merit based. People weren't saying that coaches stink and if they open up the pool more when they hire then the standard will improve (although this may be the case.)
If you are applying for a job with 2 candidates, are your chances better to get it than if there are 10? What about 20? You can say that if you're the best then it doesn't matter but that's not reality because your skills are not measured in a vacuum they are measured against the other applicants. The "best" means better than the other applicants. So if there are lots of other applicants, it's harder to be the "best" (unless you're the best possible candidate in the world I guess.)