Without falling in the rabbit hole of tolkein lore and implied lore, it is basically this. The world is constantly at war. Many people are evil. The thing they don't love is the one dude bringing the evils together. And yea, the Uruk definitely eat dogs. And babies. Anything in the "meat" category.

Like, numenor was a super shitty elitest kingdom. And the elves basically believed nothing could even potentially hurt them anymore. All the wizards are basically angels. And a balrog is just pure incarcerated corruption