How we cite our quotes: Chapter.Paragraph or Chapter.Section.Paragraph (depends on whether or not the chapter had sections - some did not)
Quote #7
"Harry [...] I as good as killed them," he croaked. "I persuaded Lily and James to change to Peter at the last moment, persuaded them to use him as their Secret-Keeper instead of me [...] I'm to blame, I know it [...]" (19.72)
Sirius's guilt makes him see himself as something of a bad guy in all of this. His own self-perception, and his willingness to do some bad things, help complicate the ideas of good and evil here. What makes people good or evil in this book? Is it their actions, their ideas, their beliefs, some combination of those things?
Quote #8
"How dare you," he growled, sounding suddenly like the bear-sized dog he had been. "I, a spy for Voldemort? When did I ever sneak around people who were stronger and more powerful than myself?" (19.107)
Sirius delivers a damning judgment against Peter here, as he basically equates Peter's cowardice with evil.
Quote #9
"He – he was taking over everywhere!" gasped Pettigrew. "Wh- what was there to be gained by refusing him?"
"What was there to be gained by fighting the most evil wizard that has ever existed?" said Black, with a terrible fury in his face. "Only innocent lives, Peter!" (19.162-3)
The contrast between the speaking styles of Peter and Sirius is interesting here. Peter stutters and asks desperate questions; Sirius speaks decisively and uses morally-charged words like "evil" and "innocent lives."