Immortality

Consider they finally invented a drug to stop the aging, what the heck will we do with all the people?

In the long run, immortal humanity would either have to revert to natural, or social Darwinism. And I don't know which of the two prospects is scarier. The first would be easier on the ethics, but the second let's you hold on to a bit of culture, preserving a veneer of a civilization. I think I'd eventually agree to the soylent green approach. Although, going the primitive route would eventually destroy the knowledge needed to stop aging, allowing the civilizing processes to start anew (once the population reduces in size, unaided by modern convention)