Comment by soandsosokrates

The distinction between moral agent and moral subject is important here.

"moral agent" is someone whose actions are actions are eligible for moral consideration.

Non-human animals are usually considered "moral subjects" or *"moral patients". Moral agents must treat them well because they can suffer, but they don't have moral agency themselves. They can be purely amoral. Their acts can be horrible, but they don't have concepts of morally right or wrong.

In the middle-ages pigs were were tried and sentenced to death for murdering humans, but today attributing moral responsibility to non-moral agents is usually considered wrong. Within humans, insanity or young age can limit moral agency. Little children are moral subjects.