[hnsucks2]

For a start, the cities you list contain many valuable people. Places doing lots of slash-and-burn farming, not so much. My original comment was a bit facetious, but if it is a civilization-ending threat (and I'm not saying it is), better to start the killing sooner when we can control who dies than collapse the whole thing and lose thousands of years of scientific and cultural progress.

[hnsucks2]

By the way, we already do this! We let millions starve to death in squalor already. Why? For the sake of civilization. Or do you think it'd be smart to ship them all over here? Amazing how timid we are about weighing life against life in a controlled fashion when this is already happening every day. We can't even have a little hypothetical chat on the Internet about it.