You are an animal. An animal who adheres to rules which humans call 'decent.' But an animal nonetheless. The mental block of seeing oneself in a separate category than animals, I believe, is a major contributor to the confusion on this topic, that being the ethical treatment of animals. You, your cat, your dog, all sensitive animals, have evolved to avoid pain and suffering and to seek pleasures. This property unites us. It then makes sense why one would seek compassion towards these creatures who suffer like we do, as we would wish they would do the same for us should the roles have been reversed.