Stephen Hawking suggest space colonization is required to prevent the extinction of mankind.  It does not take much imagination to believe this premise only a very long time horizon.  The question seems to be are we willing to invest in multi-generational projects without an imminent crisis.

Back to Hawking: He stated he was eager to get into space himself as he described how the 50,000 year trip at today’s speeds could be achieved in a human lifetime.
“Science fiction has developed the idea of warp drive, which takes you instantly to your destination,” he said. “Unfortunately, this would violate the scientific law which says that nothing can travel faster than light.” However, by using “matter/antimatter annihilation”, velocities just below the speed of light could be reached, making it possible to reach the next star in about six years. “It wouldn’t seem so long for those on board,” he said.
Where do I sign?