One does not have to be a monster, a sadist, or a vicious person to commit horrendous, evil deeds. Normal people in their everyday lives, 'decent citizens,' even respectable political leaders, who are convinced of the righteousness of their cause, can commit monstrous deeds.
This passage articulates the central thesis of Arendt's banality of evil: that ordinary, normal persons — not monsters — are capable of atrocity, and that modernity's bureaucratic conditions make this increasingly dangerous, without in any way diminishing accountability.
, Encounters with the Soul: Active Imagination as Developed by C. G. Jung, 1981thesis