This is specifically trying to be fair, rather than trying to make access equally difficult. I don't know why that is hard to grasp. I don't think 'righting injustice' is bad way to explain it.
Harvard is also discriminating against Asians because there are 'too many'. This seems quite likely but is a separate issue. The historical injustice is present, but cannot be said to have the same character. I don't think criticism of other minority AA programs is justified, but you can have your own opinion.