“Cruelty” is the default state of things. It is not a behavior we lower ourselves to, it is who we are. What we must do is rise above it.
> The Patrician took a sip of his beer. ‘I have told this to few people, gentlemen, and I suspect never will again, but one day when I was a young boy on holiday in Uberwald I was walking along the bank of a stream when I saw a mother otter with her cubs.
A very endearing sight, I’m sure you will agree, and even as I watched, the mother otter dived into the water and came up with a plump salmon, which she subdued and dragged on to a half-submerged log. As she ate it, while of course it was still alive, the body split and I remember to this day the sweet pinkness of its roes as they spilled out, much to the delight of the baby otters who scrambled over themselves to feed on the delicacy. One of nature’s wonders, gentlemen: mother and children dining upon mother and children.
And that’s when I first learned about evil. It is built in to the very nature of the universe. Every world spins in pain. If there is any kind of supreme being, I told myself, it is up to all of us to become his moral superior.’
Cruelty isn't common in the animal world, but it is very common in humans. Some animals play with their food, but they're not doing it because they get joy from inflicting pain, like we do.
As far as "an otter eating a fish alive", that's not cruel or evil, that's survival. Weird quote, man.
> The Patrician took a sip of his beer. ‘I have told this to few people, gentlemen, and I suspect never will again, but one day when I was a young boy on holiday in Uberwald I was walking along the bank of a stream when I saw a mother otter with her cubs. A very endearing sight, I’m sure you will agree, and even as I watched, the mother otter dived into the water and came up with a plump salmon, which she subdued and dragged on to a half-submerged log. As she ate it, while of course it was still alive, the body split and I remember to this day the sweet pinkness of its roes as they spilled out, much to the delight of the baby otters who scrambled over themselves to feed on the delicacy. One of nature’s wonders, gentlemen: mother and children dining upon mother and children. And that’s when I first learned about evil. It is built in to the very nature of the universe. Every world spins in pain. If there is any kind of supreme being, I told myself, it is up to all of us to become his moral superior.’
- Terry Pratchett, Unseen Academicals