i think my key issue with the sanitization of death eater characters is that it feels like people do not see their stories as tragic or empathize with the characters until we have a hc that's like "actually they were morally good the whole time!"
regulus black and severus snape are tragic characters and child soldiers no matter what side they were "really" on. even barty crouch jr, who may not have been groomed into being a death eater, is tragic when you spend a second to consider his relationship with his father. there are plenty of death eaters who we know are taking after their fathers in joining the cult. lucius malfoy, who was a prefect when the marauders enter hogwarts, most likely spread the death eater ideology, since the ideology is just a more extreme version/logical endpoint of what already existed in the wizarding world.
to me, these ideas are not headcanons, because they are heavily implied by the text. when jkr mentions malfoy in the deathly hallows that is not for no reason.
mallfoy's acceptance of snape and position of power are both highlighted in this sentence. we can infer that snape felt a sense of community for the first time in Slytherin. with malfoy as a prefect we can infer that the culture of Slytherin house lifted up bigots and those with an important family name.
this is a culture that breeds more bigotry. we know that Dumbledore did not step in to stop this cultural development in the 90s, after already seeing what it could do!!! so we can infer that he did not in the 70s. so a bunch of children were left alone in an echo chamber of hate. of course some of them became fanatics!!!
this doesn't mean they shouldn't be held accountable. but we cannot expect children to overcome cultural and political hegemony all alone. like.... that's just not how the world works. and it's tragic that children are fodder for fascist's wars, especially when the fact that the children were abused or neglected makes them more vulnerable to be fodder.
regulus and severus weren't treated as people, their humanity was denied by the fascist they served, bc that's how fascism works. exploring their characters as they are in canon, with full humanity, without needing to change their stories to see that humanity, is much more interesting to me. it is much more in the spirit of redemption and restoration.
It boils down to people refusing to show empathy for villains. The characters don't need to be whitewashed for you to acknowledge that they were mistreated or the adults around them failed them.
(What could he do?)
(Should have been a rock star)
But he didn't have the money for a guitar
(What could he do?)
(Should have been a politician.)
But he never had a proper education
(What could he do?)
(Should have been a father)
But he never even made it to his twenties
What a waste
Army dreamers
Ooh, what a waste of
Army dreamers