Why do people spend money on the space program?

It's an investment into the future. There could be tremendous benefits from space research, anything from mining the asteroids for rare materials, to establishing colonies away from a threatened earth. Someday we might use what we've learned to stop an asteroid impact. And it's not really that expensive compared to other government agencies which are even more useless. But if we have to solve every problem on Earth before we can research space, it is guaranteed that we never will.