 The idea is that we have made a “bargain” with animals to raise them, to protect them from predators and the elements, and to tend to them, but then, in return, to kill them. Moreover, the “bargain” renders killing animals permissible (defended in Hurst 2009, Other Internet Resources, and described in Midgley 1983). Such an argument might render permissible hurting animals, too, or treating them merely as tools.