It's not even about science though, It's about dreaming. If we as a country have something to push towards, something that doesn't hurt others, it's something that americans get behind, and will raise the moral of our country. This in turn will boost our economy. I think using space as an example is perfect, because unlike solving global warming (which is also necesary) it is something that we can see being accomplished immediately, you have people land on mars in one second, instead of us doing something like cutting down carbon dioxide levels (which i reiterate, it needs to happen) which will help over the course of 10 years. For something like this to boost our economy and have a profound affect on us as a country, It needs to be something that has an immediate ending, not some huge long term project.