Having better healthcare and fewer school shootings would be prestigious not spending 500 billion taxpayer dollars on getting a hunk of metal and two people onto the surface of mars, nobody else cares that's why other countries aren't wasting their time trying.
It's not the governments job to pay for technology development but industry's job, companies innovate or die, they invent and develop or get left behind, there's no way Joe Taxpayer should be paying for such experiments that's why we have stock markets and banks, ways of raising money without stealing it from the public.
On a technical level too, if Musk wants money to send people to mars he should be forced to prove he can do it with the moon, if he can't even do that reliably as NASA did in 55 years ago, then why the fuck should he be trusted to deliver on much more complex problem?
Seriously, if I was him and serious about Mars I'd be using a moon program to develop all of the technology needed for a mars project, it is out of that work that one would get the starting technology for a more ambitious mars landing. Anyone seriously trying to convince me they can do a landing on mars and back, needs to prove they can get to the moon and back routinely, else they're out the door.