But, the thing is, these ideas have trajectories. The idea that slavery is wrong or women should have the right to vote never got less accepted over time.
This cannot be the case, because those ideas have not existed since the beginning of time. They had an origin and therefore an upward trajectory towards their reification in law.
For example: Iran's official policy went from being progressive to oppressive, but it was a result of the Islamists moving into power in the 70s. They didn't just suddenly convince everybody that "hey we should oppress women". All of those people were there, and had been there for a long time. They just weren't in power.