Animals do not kill meaninglessly and aggressively. Within an animal
society, even dyads and trios, indivduals must conform to a social code
which obviously, however, differs from our social code. If you are saying
that we can not "contract" animals into conforming into our social code
you are right but it is silly to even suggest that. Actually, I think it
is outright wrong in the egocentric human sense to think that everyone and
thing should conform to self. Furthermore, animals only kill others for
food or defense. There are two and only two species that kill others of
the same kind in a ruthless manner. Ironically, they are very related
species, chimpanzees and humans (See Richard Wrangham's Demonic Males)