I'll buy that – that Sirius said things in the heat of the moment during that tense scene in the Shrieking Shack that he might regret at other points. Then again, I'm guilty of just what you say, liking these characters and thus wanting to find ways to write them as ultimately sympathetic, if flawed, people! (Definitely I've come to like Sirius a huge amount more through fanfiction, which...does that mean fanfiction is simply giving us a chance to explore the character more deeply? Or is fanfiction distorting the character from who he actually was in canon? I dunno!)

Do you really think JKR meant us to see the Marauders as responsible for their own downfall? It seems to me she has a lot of love and sympathy for them in the way she writes them, and that their tragedy is more a result of forces around them that are beyond their control. You could make that argument, though, that the mistrust and lies and suspecting the wrong person was what led to their downfall, and that the difference with the trio was that they found a way to come closer together despite their doubts and jealousies, rather than be pushed apart...