That implies that we are going to defend the rest of the planet. If anyone other than our allies wants protection, they'll have to pay for it. Of course, France will have a special rate (20 times the cost of anyone else if we even decide to entertain an offer from them).
Already doing it, more or less. This would just extend the reach further, and may lead to stronger alliances that don't require mustering troops on the ground, just a push of a button. First target: the U.N.