Not sure if someone has mentioned this, but Neil deGrasse Tyson has pointed out a critical reason why a space program is necessary.
Check out the video:
If you stop innovation, you stop progress. You stop attracting smart people to your country. Now, I'm not American, so if America falls behind, it doesn't really matter to me. But it's good to know what innovation means in practical term.
Dr Tyson also pointed out that space program also helps us learn about our own planet. For example, by studying green house effect on Venus, we may know how to prevent it on Earth.
The saddest thing is not that space program has been cut, but rather the fact that doing something great, like going to Mars, requires more incentive than scientific curiosity or because it's a good challenge. History has shown that any great undertaking has been driven by religion, war, or financial gain. Unless humanity change in a big way, we're not going to Mars until one of the above criteria can be filled. You know, if they found oil on Mars, we'll be there next month...