Jews invented racial discrimination. Let a gentile apply to a Jewish school, even if his father is Jewish and he practices Judaism they will turn him down if his mother is not ethnically Jewish.
You actually can't see the difference between religious law being used to discriminate among applicants to a private, parochial, religious K-12 school and discrimination at a public, state-funded institution based on inescapable racial identities recorded by the government at birth?
If you've been subject to the discrimination it probably feels the same. public/private whatever you call them, they are all just groups of people, and exclusionary judgment based on a couple generations of dna, well I think THAT should be reserved for haShem only. Live by the sword die by the sword, reciprocity, lex talionis, karma, ... almost always catches up.