But ... "they thought they were right" isn't an argument. Compare how they derived their bottom lines to how we have. Compare their evidence and reasoning to ours, and compare both to the kinds of evidence and reasoning that works (literally does good work) elsewhere, and the answer will probably be straightaway obvious which is the more reliable.
We have no evidence and reasoning about morality that doesn't depend on morality in the first place, is-ought problem which I won't repeat here.
Empirically, everyone derives their morality from society's norm developed in messy historical processes. Why one messy historical process is better than other by any objective standard is not clear.
By some standards we have less suffering than past times, but we're also vastly wealthier. It's not clear at all to me that wealth-adjusted suffering now is lower than historically - modern moral standards say it's fine...
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).