Ah, but politicians don't efficiently funnel money into the Earth's, or even America's problems, do they? The space program may not be the most valuable thing a Philosopher King would rationally choose to benefit the Common Good, but it's light-years ahead of the kind of stuff they actually buy.

We need a space program because, simply, we need to get off this fucking rock. Until we have humans living on other worlds, all of our eggs are in one little basket, vulnerable to being wiped out at any time by a pandemic or collision event. The fossil record shows that the longer your generation cycle is, the more likely you are to go extinct (presumably because you can't evolve fast enough to adapt to biological attacks.) Ours is 20 years, practically unheard of. The history of evolution is of big animals continually re-evolving from small ones and going extinct: it's the mice and other little guys that always survive to carry on the torch. One nasty little virus and we're history. It's somewhat irresponsible of us to keep our entire population breathing one connected atmosphere.

We need a manned space program, now, because we're collecting valuable information about how humans can survive in space. One fact stands out: humans can't live in zero-g forever, they lose bone mass too quickly. We need to be exploring engineering solutions to this, and other problems, right now. Stop putting people into space, and that learning just stops. 100 years from now the technological problem of getting an object into a space will be much easier because of improved manufacturing, design, and robotics... but we still won't know shit about keeping humans alive in space. Unless we keep trying, continuously.

EDIT: I'm sorry you got a bunch of downvotes, mrmaster2. I think it was a good question.