That night in the Shrieking Shack, Harry threw himself in front of Pettigrew to keep Remus and Sirius from killing him.
"I don't reckon my dad would've wanted his best friends to become killers."
These were the words he said. Sirius and Remus backed down, but not for the reasons Harry thought.
In truth, James probably would have understood if they'd killed Peter. If it was the other way around, there's even a chance he'd have done the same. James Potter was not the reason Sirius and Remus backed down.
In that moment... in those words... the two men saw Lily. The flash of green eyes. The prevailing sense of justice. The absolute and ruthless kindness. The fierce insistence that revenge was not a viable answer.
They reckoned Lily Potter wouldn't have wanted them to become killers, and so they didn't.
