Why is there an apparent trend in academia to paint a nicer picture of brutal cultures than is truly accurate? Its different than colonial powers ignoring their own atrocities because nobody has much of a stake in the reputation of long dissolved polities and lost cultures.
The two examples that come to mind immediately are Roman games and the Mongols. A tour guide recently explained the Colosseum to me talking about how the good the games were politically, how gladiators often survived, how animals were used to kill prisoners, and all without mentioning the killing of animals or associating gladiators with slaves. I've noticed similar views in a few books and essays recently.
The Mongolians are also suddenly portrayed as the bringers of unity and passage of knowledge while barely discussing the violence, rape, pillage, and massacres in recent literature.
What's up with this? Why are people trying to pretend that the good didn't also come with some bad.
There are a couple answers, the first I will give with a quote, from Francis Haverfield's brilliant 1901 essay "The Romanization of Britain":
In the lands that he had sheltered, Roman civilization had taken strong root. The fact has an importance which we to-day might easily miss. It is not likely that any modern nation will soon again stand in the place that Rome then held. Our culture to-day seems firmly planted in three continents and our task is rather to diffuse it further and to develop its good qualities than to defend it. But the Roman Empire was the civilized world; the safety of Rome was the safety of all civilization. Outside was the wild chaos of barbarism. Rome kept it back from end to end of Europe and across a thousand miles of western Asia. Through all the storms of barbarian onset, through the carnage of uncounted wars, through plagues which struck whole multitudes down to a disastrous death, through civil discord and sedition and domestic treachery, the work went on. It was not always marked by special insight or intelligence. The men who carried it out were not for the most part first-rate statesmen or first-rate generals. Their successes were those of character, not of genius. But their phlegmatic courage saved the civilized life of Europe till that life had grown strong and tenacious, and till even its assailants had recognized its worth.
There is a lot to say about this passage, but the crucial point here is the conception of history, as an oppositional process between the civilized "interior" and barbarous "exterior". In this conception the destiny and historical task of the civilized is to bring the barbarous under its sway, and likewise the destiny and historical task of the barbarous was to submit to civilization and then convert the other barbarous, until the whole world can sit beneath a single cafe umbrella sipping tea. Now there has always been pushback against the justness of this mission: Herodotus portrays the Scythians as being violent and brutal but possessing an appealing sort of honesty and authenticity that the civilized lack, likewise, George RR Martin portrays the Wildlings in much the same way. But the basic narrative is still there.
What you refer to is what I would say is a legitimately more modern approach of questioning whether "civilized" is actually a thing. Sure, the Germans may have raided and plundered, but they also held democratic popular assemblies, sure the Carthaginians sacrificed the occasional baby, but they tended to conduct a foreign policy of diplomacy rather than conquest. Are they really the barbarians here?
This question has a lot of significance. The colonial conquest of the world was often justified by this sense of historical purpose, that the civilized must convert the uncivilized. If, hypothetically, a modern nation were to invade another in order to alter its social structure to be more civilized, this would have echoes that go far back into the ancient past. Questioning whether the paradigm holds true for ancient times reflects on its modern application.
Now, as for your specific questions, when Maximus Decimus Meridius, commander of the Armies of the North, General of the Felix Legions, loyal servant to the true emperor Marcus Aurelius, father to a murdered son, husband to a murdered wife, etc etc, walks into an arena and slaughters twenty people with sick swordfighting skills, this has nothing to do with what happened in ancient Rome. That spectacle was 100% twentieth century America, but because Gladiator was a pretty great movie and everyone has seen it, a good tour guide would need to work to replace that image (as for the ethical concern, to do some whataboutism, come Fall tens of millions of American TV screens will watch football, well aware that in ten years half the people on the field will have permanent, debilitating brain damage due directly due to the entertainment provided).
The Mongolians are also suddenly portrayed as the bringers of unity and passage of knowledge while barely discussing the violence, rape, pillage, and massacres in recent literature.
Could you provide an example?