We investigated the effects of salient shared humanity with a benevolent or hostile human norm on perpetrators of historical atrocities. Our findings suggest that a focus on benevolent superordinate humanity enables perpetrators to legitimize intergroup discrimination and preserve existing negative attitudes towards victims. In Expt 1 (N=135), salient shared humanity with a human norm of benevolence and kindness preserved the perceived legitimacy of intergroup inequality, while exposure to a hostile norm of human nature reduced perceived legitimacy. Expt 2 (N=51) replicated the association between exposure to a hostile human norm and reduced legitimization when perpetrator intentions were unambiguously negative. In contrast, when perpetrator intentions were ambiguous, a hostile human norm had no effect on perceived legitimacy. Our findings qualify previous research, and demonstrate that the effects of emphasizing shared humanity are not equivalent or universally positive for perpetrators and victims.