Racism is morally wrong but not mathematically wrong. P(criminal|black) > P(criminal), but if you observe that someone has black skin and treat them poorly because of it, you've done a bad thing. It doesn't matter that you were just following Bayesian reasoning because you're still hurting someone on the basis of something they can't control.

Lady Justice doesn't wear a blindfold as a fashion accessory. Discarding information is a key factor in nearly every established system of justice / morality. Refusing to do so (i.e. "just" running a ML algorithm) places you directly at odds with society's hard-earned best practices.