This reminds me of this part from "The Failures of Eld Science":

"A woman of wisdom," Brennan said, "once told me that it is wisest to regard our past selves as fools beyond redemption—to see the people we once were as idiots entire. I do not necessarily say this myself; but it is what she said to me, and there is more than a grain of truth in it. As long as we are making excuses for the past, trying to make it look better, respecting it, we cannot make a clean break. It occurs to me that the rule may be no different for human civilizations. So I tried looking back and considering the Eld scientists as simple fools."

"Which they were not," Jeffreyssai said.

Maybe, analogically, it would be wise to regard the former civilizations as psychopaths, although they were not. This includes religions, moral philosophies, etc. The idea is that those people didn't know what we know now... and probably also didn't feel what we feel now.

EDIT: To be more precise, they were capable of having the same emotions; they just connected it with different things. They had the same chemical foundation for emotions, but connected them with different states of mind. For example, they experienced fun, but instead of computer games they connected it with burning cats; etc.

(Of course there are differences in knowledge and feelings among different people now and in the past, etc. But there are some general trends, so if we speak about sufficiently educated or moral people, they may have no counterparts in the past, or at least not many of them.)