Those people would likely also have access to nuclear weapons, what's your point?
I don't know what the grandparent's point was, but I believe that kinetic weapons are exempt from space weapons treaties, hence the "Rods from God" satellite designs.
I'm sure if someone wanted to destroy the earth, there are far more manageable ways to do that.
Yeah, you could just pump CO2 into the atmosphere for a couple of centuries until greenhouse effects make it uninhabitable.