I'm sure most folks at one point have pointed out to a teacher that "that all men are created equal" had a few flaws to it (slaves, women, the poor...), and often there's an argument about "well, that was normal in their day."
But the further back in history we go, more and more things look "bad," and I wonder how you as historians would suggest we thinking about and digest stories from the past. Should we consider Khan a bad person because he killed so many people? Should we consider the Egyptians bad because they held slaves? Was Jefferson good even though held slaves? Were the plantation owners of the 1860s worse for owning / punishing slaves than the Egyptians or the Romans?
I'm not as interested in a retort to a specific historical event/person, but rather how would you all advise students of history to think about historical figures. Or, what are some tips to help us see them correctly?
Some while ago, “somewhere in his writings,” Leo Tolstoy complained that “science for science’s sake is an absurd conception [because] we cannot know all the facts, since they are practically infinite in number.” It annoyed him that our understanding of the world might be “determined by caprice or immediate necessity,” and so he damned blind experimentation as a fruitless indulgence. In response, a French mathematician by the name of Herni Poincaré wrote that the point of science was not to know everything, but rather to make a judicious selection of those facts which are most interesting, those which “can be used several times, those which have a chance of recurring.” (1) It is the same for history, as for science. There are historical facts: dates, names, moments and details of grand events which have been recorded for the benefit of posterity, but it is not those facts alone which make history. Rather, it’s the process of their explanation. So, as you’ve suggested, the role of the historian is two-fold. First, they must make a determination of facts. Which are accessible? Which are reliable? Which are cogent? That being done, they must then make an evaluation of their facts. How can we understand them? Why are they important to understand? It is in answering this second set of questions that you’ll find the answer to your own question. Its nature is such that any given answer will have as much to do with the inclination of the individual respondent as with anything else. When considering any historical figure or event, people will select those facts which they find most important, and their selection will inevitably be highly biased. To address one of your examples, someone who was writing a political history of the United States might consider Thomas Jefferson as a statesman and a statesman alone, whereas someone interested in a social history of race might take particular account of his personal relationships. Neither choice is illegitimate, so long as you bear in mind the knowledge that someone else may well have made quite a different selection of facts, and therefore received quite a different world.
Disclaimer: I'm an anthropologist by training, so I'm not speaking for Historians. That said, I think Historians largely operate under this framework and that they would largely agree with the sentiment.
Cultural relativism, at least in anthropology, is not a moral position, it is a methodological position. By that I mean that cultural relativism is a way for researchers to better accomplish the goal of understanding the past, rather than passing moral judgement on the past.
The basis for using cultural relativism as a methodological approach comes down to three assumptions about society and culture:
1.) People are fundamentally rational (at least most of the time)
2.) People are fundamentally moral (at least most of the time)
3.) Morality is culturally specific/relative
If you follow these propositions it stands that, perhaps given a few exceptions, no one sees themselves as a villain or does something because it is morally wrong. There are no mustache-twirling villains in history, just rational people trying to navigate a complicated world based on the tools they have available to them to do so. Often, these tools - moral systems and worldviews - are contradictory and conflicting, but at the end of the day the position of the researcher is that everyone in the past was trying their best to act in a rational and moral way however they understood that to be. Even when a person is actively bucking the conventional morality of their society we can say that they are acting in a way that they think is most rational.
Consequently, it would actively hinder my ability to understand why people acted in the ways they did in the past to pass my own moral judgement on their actions since they did not themselves see their actions in that way.
This doesn't mean that, in my capacity as an individual, I can't find certain behaviors and ideologies to be morally wrong. However, the goal of history is the understand the "whys" of history and casting moral judgement on the past actively impedes that goal, so I should be sure not to make those kinds of judgements in my capacity as a researcher.