To insult someone we call him ’bestial. For deliberate cruelty and nature, ’human’ might be the greater insult.

Asimov contrasts the common insult “bestial” with the reality that calculated, purposive cruelty is characteristically human rather than animal. Animals may be violent, but their aggression is typically tied to survival, territory, or instinct; “deliberate cruelty” implies reflection, choice, and often ideology—capacities associated with human cognition and social organization. The sting of the remark is moral and linguistic: our metaphors misplace blame by animalizing brutality, when history suggests that the worst atrocities are enabled by distinctly human traits (planning, abstraction, dehumanization, obedience to systems). The quote thus functions as a critique of euphemism and a warning about self-exculpating language.