They know what. It's the why and the how to stop it that seem to be a little more fuzzy.
He hates humanity. He hates us for even existing and being loved by his Father. You know. THAT Father. Think of him like a psychopath. The kind who doesn't just kill his victims but torments them before doing so. We, as normal people, think that's sick and demented and wtf is wrong with this guy. But him? Perfectly normal. And he doesn't even have to do it all himself, that's what he's got demons for.
And I know you will. Because you're one of the bravest people I know but you don't bloody well know that yet damn