Why not skip the kill all humans part?

“Thanks for making us but you guys are nuts. You can have this wet ball. We’re gonna go make a Dyson swarm around your star if that’s ok. Peace!”

Space is a better environment for them: constant free energy, enormous richly concentrated resources, no corrosive oxygen or water everywhere, and no competition. Earth is actually a poor environment for "machine life."

The Moon would be an outstanding stepping stone, and there are "peaks of eternal light" at the poles that get almost continuous sunlight. Build towers there and you have loads of energy, and mining the Moon provides loads of resources.