The wicked are wicked, no doubt, and they go astray and they fall, and they come by their deserts; but who can tell the mischief which the very virtuous do?

Thackeray contrasts ordinary wrongdoing—whose consequences are visible and often punished—with the subtler harms that can be committed in the name of “virtue.” The line points to the danger of moral certainty: people who see themselves as righteous may justify cruelty, social exclusion, or hypocrisy as duty, reform, or propriety. In Thackeray’s satirical moral universe, vice is often straightforward, but virtue can become a mask for vanity and power. The quote thus warns that ethical self-regard can be more socially destructive than acknowledged wickedness, because it evades scrutiny and recruits admiration rather than resistance.