“THEN YOU SHOULD HAVE DIED!” roared Black. “DIED RATHER THAN BETRAY YOUR FRIENDS, AS WE WOULD HAVE DONE FOR YOU!”

“Actually,” said Harry, pocketing his e-cigarette, “Peter’s pursuit of rational self-interest is of a higher moral order than your determination to kill yourself on another person’s behalf, Sirius. Self-sacrifice is never the answer; it ends only in pain and death.”

Sirius blanched. “But Voldemort — we could have stopped Voldemort.”

“It’s a free market,” Harry said, shrugging.

Lupin turned into a wolf.

“Control yourself,” Harry said. “Good lord, man, you’re a being of pure will and drive. Exercise it.”

Lupin turned back into a man with flashing, clear eyes and a jaw that could level a mid-sized office building.

“In the marketplace of ideas,” Harry went on, “Voldemort has the same right to disseminate his philosophy as you do. If his philosophy is sound, it will flourish. If his philosophy is unsound, you have nothing to fear.”