What happens to a dystopia that never comes to be? Does a story’s inaccuracy in predicting the future make it kitsch, a curio with no value beyond historic curiosity? Is an unrealized world the science fiction equivalent of a doomsday prophet after doomsday comes and goes? Or is there still something to be gleaned from a dark vision that might have gotten some particulars spectacularly wrong, but still taps into a broader understanding of how the future might go awry, and suggests what we might do to keep that from happening? The 1972 science fiction film Z.P.G.: Zero Population Growth imagines a world destined to die not by fire, but by overcrowding. Set sometime in the early years of the 21st century, it takes place in a world undone by a population explosion, a development that has led to skies choked with smog and the mass extinction of virtually every animal and plant species. Those disasters have led the World Federation Council to impose a 30-year ban on childbirth. The WFC enforces its edict strictly but reluctantly, seeing it as the only hope for Earth’s survival. Sure, it might suck to force citizens to submit themselves to mandatory abortion machines after intercourse, and to be forced to use domed “execution chambers” to dispense with anyone who has a baby — a crime that means death for both parents and their illegal child. But what else can you do?