They would look at us as moral degenerates. But despite this, our society manages to function quite well, roughly.
Correspondingly, we think our ancestors are the bigots.
I don't think that's true at all. It's only true if "roughly" means "for specific kinds of people". I think that clause is necessary for the sentence to be true. And with it, we've contradicted the statement "our society generally functions well".
Absolutely. 1966 was terrible in many ways compared to today, but it was a much better world to live in than 1916.
Is that really how we should judge it? I can imagine a society full of slavery functioning well according to some measure. Does that say anything about the morality of slavery?