In The Humanitarian Theory of Punishment, Lewis challenged the increasingly popular idea that criminals should never be punished because they deserve it. Instead of treating crime as a moral act committed by a responsible human being, the humanitarian theory treats criminality as a disease to be cured by experts. Lewis warned that this supposedly merciful approach could produce something far more arbitrary and tyrannical than traditional punishment: indefinite confinement, forced psychological treatment, the denial of moral agency, and even the punishment of innocent people in the name of deterring others. Mercy is indispensable—but mercy only makes sense when justice comes first.