where his civilizations, including our own

I think the main distinction between the Twins and the Marauders resides in whom they were picking on: the Twins hex people who seriously annoy them (like Zacharias Smith), and play pranks on the general public (or even for the general public's relish - cf. OotP!) and Professors. There isn't one particular person they persecute (apart from Percy, but we all know siblings are fair game!). Whereas the Marauders used Snape as, basically, a punching-ball! And that is what makes them guilty, in my eyes - the persecution of that one particular person, who, however disliked or an "oddball" he was, had never deserved it! (I also have strong issues with the description of Snape as an oddball by Sirius, primarily because I have always enjoyed being called 'weird' and 'odd'... Maybe I don't understand the English language perspective, but I don't see why "oddball"=nasty!) (I do, though, understand that Snape was nasty, but because he was "up to his eyes in the Dark Arts", not because he was "thaT little oddball")
For the record, I am by no means a Snape fan, I love Sirius and Remus (I have less sympathy for james, though), and I thouroughly enjoy the Twins.
~Alya~