Animals For Food

I am not sold on the pain/pleasure justification for equality, from Singer's argument of humans and nonhumans should have equal consideration of interests (capacity for pain/pleasure). Especially with nonhumans, and even more so with instant death (or killing), as opposed to prolonged suffering. If one can justifiably kill in animal, once killed, it does not know or feel pain or suffering upon death. Of course the capacity for pleasure is taken away, but this is not known or felt upon death either. How can one justify killing the animal in the first place? I think with the lone intention of killing the animal for food. I think we are obligated to treat animals with respect and to not make them subject to suffering, however, if one makes animals a part of one's diet and always has, killing the animal for this purpose is in the nature of many humans, as it has been done since our dawn. I think animals which we make a part of our lives on an emotional level, etc. such as domesticated dogs and cats, and humanize them to a sense should not be killed for food, and the same applies to endangered species, which may play a vital role in the evolution of the planet and of our own species, as well as many others. If one species is removed, it effects many other components of life (ie. remove sharks, smaller fish populations explode, which will consume larger amounts of phytoplankton, which supplies most of our oxygen). Not much of an argument yet... but its my intuitive thought on the matter, and maybe I can build an argument as the class moves forward.