Too many examples to list and I encourage you to do your own reading, but a low-hanging fruit is the ongoing legal battle of Students for Fair Admissions v. President and Fellows of Harvard College. Policy which was intended to make admission standards more equitable have succeeded in making them shockingly discriminative.

As I said, everyone involved I assume was acting out of good faith, but it's incredibly easy to see in retrospect how misguided their decision making was.