Suppose medical technology advanced to the point that it was possible to prolong life indefinately. People could live forever, and maintain clear thinking, decent motor skills, and generally all around good health. Not only that, but this new miracle is affordable enough to be available to the majority of the population of the entire planet.
Unfortunately, one of the side effects of said drug is that it makes the user infertile. You take it once, and you're done, no more offspring.
What then? How do the governments of the world distribute said drug? Should they force certain people not to take it for the purposes of procreation? How do they deal with certain sections of the economy which are soon to take massive hits (like teaching, toys, baby forumla, etc.)?