I don't think people vilify Sirius - the fandom, or the corner of the fandom I know, seems to adore him (as I do). The thing is, Sirius may be a good guy but he's not exactly a role-model despite his many admirable qualities. He does have a dark side, as would anyone after fighting a war, losing his best friend and feeling responsible for it, failing to recognise that one of his closest friends was a traitor to the cause and spending a decade in Azkaban! Not to mention as a young boy he was arrogant, prone to that sort of casual teenage cruelty that I always found horrifying, and the type of hot-headed, erratic, wild character that could easily make a rash decision and have it backfire spectacularly.

Going back to Grindelwald, one has to wonder if, considering his being expelled from school and his eagerness to throw Unforgivables around when he'd lost his head, he was similarly wild and unpredictable in his youth (I think Dumbledore implies it in DH?) - that coupled with a total disregard for school disipline but none of Sirius' empathy or strong attachments to his friends just screams Teenage Psycho in the making!