From the remarkable H. G. Wells, in a 1902 lecture at London’s Royal Institution:
“It is conceivable that some great unexpected mass of matter should presently rush upon us out of space, whirl sun and planets aside like dead leaves before the breeze, and collide with and utterly destroy every spark of life upon this earth… It is conceivable, too, that some pestilence may presently appear, some new disease, that will destroy not 10 or 15 or 20 per cent of the earth’s inhabitants as pestilences have done in the past, but 100 per cent, and so end our race… And finally there is the reasonable certainty that this sun of ours must some day radiate itself toward extinction… There surely man must end. That of all such nightmares is the most insistently convincing. And yet one doesn’t believe it. At least I do not. And I do not believe in these things because I have come to believe in certain other things–in the coherency and purpose in the world and in the greatness of human destiny. Worlds may freeze and suns may perish, but there stirs something within us now that can never die again.”
Of the three outcomes Wells gauges to be most fearsome for mankind’s future, the first is the most telling when it comes to encouraging interstellar research. We know how many massive impacts from asteroids and comets have caused species extinction on our planet, and there is no reason to believe such events could not happen again. That means we need a space-based infrastructure in the outer Solar System to intercept and alter the course of objects likely to hit the Earth. The technology developed in building that infrastructure will make possible our first probes to nearby stars.