Easy people.
Human beings killing even human beings is wrong. But it is more understandable to kill another human, out of hatred perhaps. Out of love, or revenge. These are human emotions, so it is more understandable. Whereas killing cats or puppies, or any type of animal, if it isn't to help out survival, isn't understandable. It's like saying the cat had a choice not to be put in the trash can. It's a cat. Cats aren't exactly as smart as we humans are. It had no choice, because of a greater species.
But we aren't a greater species. We have so much intelligence, but at the same time, we all do things wrong. We all act bad at times. We do stupid things all the time. Hurtful things, and harmful things. Other species don't do that. They hardly ever act out of character to their own instincts.
Animals are more intelligent. Because they do what they do to survive alone. Humans do things stupid to survive. Stealing and such. We do things to survive, that are going to hurt other people. Humans are selfish, entirely. And animals are not as selfish.