As a capitalist, I'm an very much in favor of it. One of the biggest arguements against it is that it diverts money from other programs. i.e. how could you think about spending $10B US on a space program when we have some many homeless and starving people?
The main reason, in my mind, is that the money spent on space has historically caused economic growth. that $10B may yield $100B in economic growth - more money for more people. There are many many many jobs created in the process.
We also get the benefit of improving our understanding of the universe and that's never a bad thing.
