Oh, no, I didn't mean we'd try to nuke the aliens. I mean we'd threaten to nuke ourselves: irradiate the planet until it's incapable of supporting life (including the aliens' life), if they tried to exterminate us.

"Attack and the planet gets it", see?

Of course we get it along with the planet, but I'm assuming that if the aliens are invading they're planning to exterminate us anyway.