Buddha taught that human beings should not harm any living thing. We should even avoid stepping on an ant. As I explained in the article, he commended a vegetarian diet for this reason. (Plants are alive, but it is permissible to eat them, but we wanted humans to refrain from harming any animals. Not only should we not eat them, but we should not use any parts of their body for our own uses--no using hides or skins for clothes or shoes, no using bones for tools or ornaments, etc.
I agree with this because if a person can mistreat an animal or take an animal's life because it suits him, then that person becomes coarsened and will thus be more likely to hurt other human beings.