I brought this up before, but people sort of ran with the southern myth (as annoying as it is...)
I get irked by the "fallen utopia" myths, the idea that a conquered, or now no-longer existent culture, lived in a perfect harmonious utopia, before largerm evil (insert name of an expanding Civilization at the time) came along and conquered/killed/culturally absorbed them.
I see this all the time, looking at history with rose tinted glasses. I believe this does those same cultures a disservice, by painting over the gritter, dirtier, parts of their history. Many times I find it's in the same mindset as jingoisim, albeit a weird psudo-historic counterpart.
I'll use a less sore reference.
Celts & Norse I find them fascinating, but often those who idolize them in story and prose leave out the more brutal aspects, or play them off as "oh those cheerful scamps" so they conform to the "pirates that don't do anything" trope in pop culture.
There's a line in the Danish rune stones where Viking logs call one warrior "the child's man" and find it both hilarious and a threat to his masculinity that he refuses to kill children during raids.
Or that there's actual evidence that Wicker Man rituals were preformed as ceaser said, where rather than assisting enemy wounded, or taking captives, they sacrificed everyone, including camp followers, captured. To ensure a bountiful harvest.
I find these things compelling, and the reasons behind them revealing. Just as norse myth and storytelling or celtic song and poetry, is compelling, and revealing. I believe it does a serious disservice.