> But if it was obvious that it was wrong, why did masses of people agree to this? They wouldn't have done it if they also saw it as wrong.

Because we, as a species, learn.

Yes, value systems might change. But it seems, at least to me, that they rarely (not never, but rarely) revert back to older norms.

We probably are "wrong" about things we believe right now, too. Some of the beliefs will be considered wrong in the future because we have different circumstances. Most of them will have changed because we've realized they're actively harmful to the continued existence of a human society.