It is sometimes said that cruel yet short wars are better for humanity than restrained yet lengthy ones. The idea finds sympathy among Francis Lieber and his Prussian contemporaries, as well as some modern writers who back selective non-compliance with international humanitarian law (IHL) on act-utilitarian grounds. This article refutes three underlying claims and reaffirms that IHL progressively narrows room for crude interest-balancing by its duty-bearers. First, it is claimed that toughening wars quickens them, whereas moderating wars prolongs them. This empirical claim overlooks how actions of the party resorting to brutality – the “brutalizer”, for short – interact with the intention of its adversary. Although the brutalizer clearly controls the amount of violence that it chooses to inflict on its opponent, it does not control the opponent's will to resist and, consequently, the length of the war it fights. History abounds with instances where adding cruelty has stiffened the enemy's resolve rather than accelerating surrender. Second, it is claimed that ruthless but swift wars lessen net inhumanity. On this act-utilitarian view, it is normatively superior to hasten wars through barbarity than to lengthen them through moderation; it is therefore the brutalizer's responsibility to toughen fighting and the brutalized party's responsibility to refrain from resisting the brutalizer. Problematically, the brutalizer usurps authority by imposing its own utilitarian considerations upon the brutalized party. Moreover, the brutalizer blames its disobliging adversary for the extra bloodshed to which it resorts in the name of maximum utility. Third, it is claimed that IHL does or should permit non-conformity when non-conformity stands a reasonable chance of increasing net humanity. This position is inconsistent with IHL's functions, however. IHL does aim to reduce net wartime harm, but it would be a mistake to assume that utilitarian ends necessarily justify, let alone require, utilitarian means. When IHL enacts unqualified rules, it predetermines their conformity or non-conformity through processes that are distinctly not act-utilitarian. Nowhere in these processes do lesser-evil justifications naturally belong.