The two things can be separated; GR Elton saw the duty of historians as empirically gathering evidence and objectively analysing what the evidence has to say. Even the Walloons manage (just) to acknowledge that Wellington won Waterloo!
People at the time were shocked and horrified when they found out about the concentration camps, so that isn't imposing the mores of today. Are you my son? We have this discussion all the time at home; one of the joys of having a son with a First in History and an MA as well. We can't erase the past; we cannot change it either. We can examine it dispassionately (or not) and see how it shapes us now, what we should take from it, and what we should discard. I don't think we can understand the past if we try to judge it with the mores of today or through the lens of today either.
I had a discussion once online with a 20 year old who was very critical of the WWI generals, and they should have known 'x' 'y' and 'z'. Trying to point out that there were delays in communication, no satellites, radar, very little aerial surveillance etc fell on stony ground. He could not wrap his head around the fact that surveillance and comms were very different in Flanders in 1914-18 from say Kosovo or Iraq all those decades later and that the immediacy of modern communications and computer driven defence analysis were not available. The WWI Generals did not have all the information available to a modern Commander today and thus their decision making was, to his eyes, lacking.
It's not just our mores that we consciously (or unconsciously impose), but we forget at times that there weren't bathrooms, inside loos, quick methods of communications, health care; all the things that we take for granted today. Life was ‘nasty, brutish, and short’ to quote Hobbes and without the scaffolding that shores ours up. We try to judge or examine the past from a place of infinitely greater comfort than ever existed before and I don't think that necessarily works.