Very little of the great cruelty shown by men can really be attributed to cruel instinct. Most of it comes from thoughtlessness or inherited habit. The roots of cruelty, therefore, are not so much strong as widespread. But the time must come when inhumanity protected by custom and thoughtlessness will succumb before humanity championed by thought. Let us work that this time may come.

Schweitzer argues that much human cruelty is not driven by an innate “cruel instinct” but by unexamined routine—social custom, inherited attitudes, and simple failure to think. By shifting the cause from nature to habit, he implies cruelty is neither inevitable nor irresistible: it persists because it is normalized. The quote then makes an ethical and political claim: humane progress depends on reflective moral consciousness (“humanity championed by thought”) overcoming the inertia of tradition. The closing appeal—“Let us work”—turns diagnosis into responsibility, urging deliberate, reasoned effort to reform institutions and everyday practices that shelter inhumanity behind convention.