Okay, substitute crazed survivors for the second of the three plagues, and famine for the third. Assume that both of these kill 90% of the people at the time.

Okay, substitute crazed survivors for the second of the three plagues, and famine for the third. Assume that both of these kill 90% of the people at the time. That still leaves 7 million humans on the planet, and the ones most likely to be left at the end of that are also those most likely to have already dealt with basic security and food. My point wasn't that it would be a good thing, just that killing ALL humans is a much harder task than it sounds.