^ Pretty much this. If you announced tomorrow that we're going all manifest destiny on the cosmos and we're headed out to Mars and the Moon and beyond for gold, exploration and what have you you'd find no shortage of volunteers.
But you would face a shortage of investors, which is kind of the problem.
^ If you're doing it the idiotic Weyland-Yutani way. If you do it the old-school state-sanctioned settling and exploration you'll have no shortage of investors because you can make all the investors you want then.
It's basically how the frontier got settled in North America.
In that case you will face a lot of political resistance (actually we already do).
The problem with the frontier approach at the moment is technology differences. People were able to travel from east to west in a covered wagon with a 2/3 chance of survival. If you managed to convince thousands of people to start building rockets and try and colonize the moon, we'd be lucky if even 1% survived. We simply don't have the technology for individuals to participate in any form of space race.
On the other hand, if what you mean is "get the public fired up so that they donate to space programs and convince their politicians to do the same," that's another thing, and is perfectly plausible. The comparison to the Gold Rush is just throwing me off.
So... we can't go into space because we don't have the technology, we don't have the technology because we don't have the resources to spare and we don't have the resources because we can't go into space?
Who are you responding to? If it's me, then: Individuals can't do into space. You need the money and resources available to governments and corporations to do it. Those are the ones you need to convince it's worthwhile.
But they don't want to do it themselves because they don't have enough resources to spare. Basically, the resources they need to go into space are in space.
We put 12 men on the Moon and brought them back safely on engineer's slide rules, primitive computers and good old fashioned balls over 40 years ago and we didn't know what the fuck we were doing back then.
We can do more and better than that. Technology isn't the problem, it's limp-wristed people afraid of even so much as a risk of anything going wrong.
You really think if some random unemployed guy with no engineering training tries to build a rocket to take his family to the moon and start a new life, it's not going to literally blow up in his face? And even if he gets that part right, that he won't make a mistake when building his habitat on the moon, thus killing everyone inside? Or screw up the hydroponics and starve to death? So on and so forth.
Look, I'm one of the biggest proponents for space exploration. I've actually considered the idea of the government just grabbing random volunteers, training them, and using them to populate a moon base. It could work, though we don't have anywhere near the political will to get funding.
But there's a huge difference between putting ordinary people in an artificial environment built by experts (hopefully with those experts still around to help and train the newbies) and expecting the ordinary people to do everything themselves.
If they don't have any other choice—say, there's a plague or other massive planetary disaster on Earth and they need to flee—then people could flee the planet with modern technology, without help from the government. But SO many of them would die. SO many. It would make the bodycount of the Gold Rush look cute.
Fun fact: Most folks won't be building their own rockets. (If they want to though I ain't gonna stop em.) However political will is easily manipulated into such an endeavor, after all Bush mustered the support for Iraq in 2003 and Clinton the Balkans in the 1990s (while mired in rumors then impeachments). Getting support to lay claim to the Moon, Mars and beyond would be trivial in comparison to that.
Indeed, and these days, with better materials all around we could probably do it much more cheaply than back then. Hells, the Falcon Heavy (due to fly next year) would almost certainly be good enough to redo the Apollo 8 mission.
Though if they do I reserve the right to call them Jebediah Kerman.
The problem is that it's incredibly expensive to send human beings into space. And the return on investment isnt seen for years, at best. It's a very large up-front investment with a very high risk of not seeing a profit. No one has any reason to take such risks, at least not yet.
Now, political impulses like nationalism are another story...
^ That's why I said you don't do it the idiot Weyland-Yutani way.
It's so expensive that right now, there is no way at all. American taxpayers certainly show little interest in it.
American billionaires OTOH... Remember, of the seven tourists to have visited ISS, two were born-and-bred Americans and another three were immigrants.
It's cheaper than the (broken) welfare state and unlike a lot of government activities the past 10 years it would have a positive effect in both economics and science.
American politicians show little interest. There was a lot of support for Bush's goals to go back to the Moon and beyond at the public level. That's been one of Obama's actions that is universally regarded as a complete failure by everyone. Cancelling Orion was a horrible idea, no two ways about it.
A bad asteroid impact with global effects would kick people into finding new places to live.
One of the key factors to population movements is opportunity for profit. During the 1849 California gold rush the population of San Francisco grew by an order of magnitude. If someone can establish profitable asteroid mining or orbital farming and industry at the langrage points then it's possible for a massive extra planetary migration to take place. People walked to California with a 2/3 chance of survival over a six month trip. People will suffer any hardship if it means a better life for them and their families.