Good Counter Arguments Against Defunding Space Exploration

These are the best arguments I've seen in favor of space exploration even in tough economic times. Quoting again (as I did last week) from the "Starship Asterisk" forum (the discussion site for the much loved Astronomy Picture of the Day), someone said:

"The money should be instead used for disease research, such as a cure for cancer."

...and someone else added:

"I would rather have a (much needed) subway line in my area than another rover on Mars."

The replies were:

"No planetary mission has been mounted that didn't return a wealth of new information- much of it applicable to our understanding of the Earth as well. And of course, the money invested in these programs isn't thrown away, but is spent developing new technology, and helps the economy both directly and indirectly. 

"It's a mistake to think that you can't invest in space exploration without also investing in other areas of research. And realistically, if we were not spending this money on Mars, I doubt very much we'd be spending it on disease research. That's not really how scientific budgeting, or budgeting in general, works in this country."

and...

"Are we really going to argue about the relatively insignificant amount of money that NASA's amazing projects take again? If $2.5 billion dollars could cure any disease it would have been done a long time ago. 

"For that matter, why don't you take that $2.5 billion from the $21 billion Harry Potter franchise? Or the $5.6 billion NCAA budget? Why should we have movies, books, or basketball when someone out there has cancer or needs a subway line?"

and...

"I'd rather have another rover on Mars than a subway in your area! (Seriously, there's no chance that money which doesn't go to NASA would ever be used to build a subway line.)"

Not all the logic is airtight. NASA is, of course, funded from public coffers, unlike Harry Potter or basketball. But if we're talking, generally, about where humanity ought to spend its resources, then, yeah, space exploration is at least as important as that stuff. Perhaps we should be spending every last dollar to heal our sick and feed our hungry (in fact, strike that "perhaps"). But we don't. And as long as we're going to be selfish and frivolous, space exploration, like all science, deserves its tiny slice of the pie.