Tu quoque (whataboutism)

Biological Parallel

Cleaner wrasse inspect client fish for parasites but sometimes cheat by eating protective mucus instead. When caught, they immediately switch to eating parasites—but clients who have cheated others are more tolerant of being cheated themselves. This reciprocity tracking creates mutual tolerance of defection among defectors. The 'you too' defense exploits our evolved sense of fairness: if punishment is hypocritical, it threatens coalition stability more than it deters cheating.