>Massive environmental destruction doesn't seem to bother them, so long as the people are starved and dehydrated to death.
You give them too much credit. They have no lofty goals, not really. They're trying to scratch the itch of a lust that permeates their being. An itch that can never be scratched.
They lust after destruction of all Life. They need the max suffering of all to convince themselves they are alive, when they're dead already, just for the choices they've made.