Gregor sees a mouse, attacks it, plays with it, kills it, and, if he is hungry, eats it. That, simply, is what he does. Why, then, is what I do so hard, so complicated, so unsimple? Why cannot I, simply, do what I do?
They were not abstract pigs. They had faces and attitudes and personalities. They had lives that she had witnessed and documented just before seeing them killed.
The ultimate purpose of my farm, though not the whole point, is to raise animals to be slaughtered so that we can eat their meat. Though it is arguably better to treat an animal as an animal rather than a widget, in either case we are assuming that an animal does not have the same capacity for feeling as a human.