If a manager and company have any justification for pay differences that are not due to protected classes, then they have nothing to fear. If they do pay people differently because of protected classes, they may run into trouble, but I think that's okay.

If most companies were transparent, employees would be a lot more knowledgeable about what leads to more pay. I think we would see more negotiation and engagement and healthier conversations about money. People would be upset at first, but once we start collectively understanding the legitimate reasons for pay discrepancies, and we eliminate the illegitimate ones, I think most people would be happier.