Aristotle and Aquinas on Happiness

Aristotle and Aquinas thought that happiness was an activity, not a feeling. That is a thing that makes a big difference between most popular forms of ethics today. If the fundamental principles of ethics depend on pleasure and pain, then animals must belong to the same moral community since they can feel pleasure and pain. But it doesn't follow from that that you can mistreat animals because we can have obligations to creatures that aren't part of our own moral community.