We tend to feel that we have the right to live but other creatures don't have the right to live equal to ours. We feel quite comfortable killing things that are annoying and get in our way. It is not a healthy philosophy. Killing anything, regardless of the reason, regardless of the justification, diminishes us. The prime directive should always be to make the effort to find a way to not kill something in our effort to get what we want. Taking pleasure in killing something is not good. Killing something unnecessarily is not good. It's always best to spare life rather than take it, to recognize that we are all part of the animal kingdom and we all have a right to live.