A lot of what any government does is a rounding error on the overall budget, but are still absolutely vital. Those rounding errors don't half add up quickly. I'm pro-space exploration and believe it's worth funding, but this particular argument doesn't strike me as useful. Space exploration and technology development should justify it's costs on the same basis as any other government programs, any number of which of which could be revolutionized by 'small' increases in the overall budget.

If instead of increasing military spending 54 billion, we gave it all to NASA, we could be quadrupling NASA's budget.

NASA should pass it on to Elon.

If we establish a permanent Mars colony, that would really increase security for all of mankind.

Building more nuclear weapons is NOT increasing security.

The risk is that more money does not always mean more progress. Government organizations tend to grow all by themselves (would be interesting if you could legislate some productivity targets into budget expansion maybe?)

Why is it so important to send people on these missions outside of some 21st century version of manifest destiny? NASA could do so much more with its limited funding if it just cut out all the humans.

Carl Sagan used to make that point. From a science perspective, you get a much, much better bang for your buck sending robots. But as Larry Niven pointed out to Sagan, every time you convince someone that manned space doesn't make sense you convince them there's no reason to go into space at all. Yes, NASA could do a lot more with its budget if it didn't do manned space, but if it didn't do manned space NASA might not exist at all.

  > every time you convince someone that manned space doesn't make sense you convince them there's no reason to go into space at all

That's just well-sounding nonsense. People can appreciate science and exploration even if it does not involve video of humans in outer space. Video or photos of celestial objects are enough reason for the laic public and there are many physical measurements that should be done to advance our knowledge. All this can be done very well and cheaper without humans onboard.

This mission's passengers appear to be funding it, at least in part.

In that case we're using the wrong word. Tourists go on "tours", not "missions".