We're going to need a LOT more killer drones people.
Yes, really. Once resources become scarce enough, and suddenly a catastrophe eliminates a large chunk of them, there will be a lot of people fighting for survival and a share of the planet's resources.
(Idea: the government should tax us for clean air and clean water. It costs money to add pollution controls. People should have to pay for it. You don't think clean air grows on trees do you?)