Men do not differ much about what things they will call evils; they differ enormously about what evils they will call excusable.

Chesterton is pointing to a common moral pattern: people often agree in the abstract about what counts as wrongdoing—cruelty, dishonesty, betrayal, and so on—but diverge sharply when judging particular cases, especially those involving themselves, their friends, or their favored causes. The real battleground is not the definition of “evil” but the granting of exemptions: the stories we tell to make an acknowledged wrong seem necessary, understandable, or “not really that bad.” The line critiques moral double standards and the elasticity of conscience, suggesting that ethical integrity is measured less by what one condemns in theory than by what one is willing to excuse in practice.