It's disappointing that space efforts have struggled against "spend the money here instead" obstructionism from almost the very beginning. Even back in the mid-60s—arguably during NASA's heyday—Congress looked at NASA as a bag of money they could raid to pay for other projects with little loss of political capital. And they (plus Nixon) did just that at their first opportunity. It's an easy target, even more so than most federal science funding, precisely because many of the benefits are sufficiently long-term that the politicians who first voted for space projects will be long retired by the point where they're obvious. People love looking what NASA accomplishes, but they don’t really give much of a damn beyond a general sense of pride in their accomplishments.
Wanting to make the world a better place is nothing new. It’s an obviously desirable goal, but can we at least pretend to be realistic about it? Just going by the list of desired outcomes you’ve provided, you’re proposing a radical realignment almost every significant aspect of our economic, political, and social systems as a species. These might not be difficult engineering problems (well, not directly, at least), but they are by no means simple things. And for all the problems that free markets might have, they’re also very good at solving many others.
Literally no one is proposing that we go and terraform Mars, Titan, or any other planetary body anytime soon. These are all significant, long-term efforts that won’t be possible for well into the future, and they presuppose the existence of significant space-based industry that hasn’t been built yet.
Any terraforming proposals are for well into the future, and presuppose the existence of significant space-based industry that hasn’t been built yet. By the time that comes around, our industrial capacity will be—by necessity—far greater.
Even today, the opportunity cost associated with space exploration is a tiny expenditure at only 0.5% of the US federal budget. For decades, NASA has worked on a shoestring budget, with their hands tied by the demands of congress, revolving presidential administrations, intelligence agencies (look at how their hypothetical mission requirements dictated major design changes for the Space Shuttle), and an apathetic public.
Space exploration isn’t just for the enjoyment of space-groupies and science-fiction fans. There are real-world benefits, and access to a growing space-based industry gives us a host of new options for dealing with global challenges.
No matter how charitably you look at efforts to curb greenhouse gases, it’s very likely that we’re going to need to look at large-scale climate engineering efforts to deal with the consequences. And if we’re hoping to industrialize underdeveloped nations, thereby helping counteract some of the global wealth disparity you’ve mentioned, we’re going to need climate engineering because those efforts won’t all be clean ones. Space-based solar power could help deliver even cheaper, more efficient renewable energy that sidesteps many of the problems faced with terrestrial solar receptors. The efficiency demands of any space colonies would spur continued research on genetically modified food crops, even beyond what would be economically viable for purely Earth-based farming. Plus, we’d likely see further development of crops similar to golden rice in an effort to simplify a colony’s food production needs. Despite the hysterical overreaction to golden rice on the part of certain activists, such improved crops could have a significantly outsized effect on the health of peoples in impoverished nations. Better yields, and hardier crops able to be grown in a wider variety of conditions can also help local farmers overcome some of the logistical difficulties they currently face.
And that’s completely ignoring the very real threat of impact events. As it stands right now, we do not have the capability to deflect an asteroid that’s on a collision course. While the overall risk of a major impact event might be low, the potential consequences are pretty scary. No matter how you look at it, we’ll eventually experience another impact event. It’d be nice to avoid losing a city or two, or worse, when that happens.
I guess my point is this: even if we pushed for a major increase in space spending, it’s still a tiny, tiny fraction of the 2014 gross world product (GWP) of approximately $107.5 trillion (PPP). It’s as close to a rounding error as you can get when you’re talking in terms of billions. And while there’s always an opportunity cost, that money doesn’t exist as a separate lump sum that can just be redirected towards another project that you find socially acceptable. Nor does investing in space mean leaving Earth behind and repeating the mistakes of the past elsewhere.
It means giving humanity more options, increased industrial capacity, and technological advances that can be applied to other problems. There is literally no reason why humanity can’t continue to work towards more sustainable (however you want to define it) practices, while simultaneously expanding its space presence beyond LEO. It’s the very definition of a false choice.