@Riger
"just for the fun of it"
Not entirely true either, at least aside from psychopaths who actually do enjoy that. The game of life isn't just about eating. For example, hunting the Dobuwana to extinction isn't just "brutal and murderous", it's ensuring the victory of humanity by removing their main check, as you said.
As for domestic cats, they've been kept as pest killers for ages. It's basically their job to kill small creatures. Just like how duck hunting dogs will kill birds yet not eat them, it's how they've been wired.
@ZeroLight315
You'd think so, but typically a predator only goes far enough to render the prey unable to fight back. They don't deliberately deliver the killing blow, they don't need to. By the time they're eating them, the prey usually can't even flail around.