I have heard the tired argument that we can use that money to fix things on Earth for my entire life. The western economies have massively spent more money.
Things have gotten worse.
What things? Worse for whom? Compared to when? In many measurable ways (lifespan, infant mortality, comfort, nutrition, education, individual rights, especially for women, violence, medicine, communication, sanitation, etc.) "things" are vastly better for most people than they were 100, 200, 400 years ago.
We absolutely should spent money on manned space flight.
There are enormous resources in space and the key to clean energy. Factories and data centers can be moved.
There are unquestionably enormous resources in "space", given that "space" encompasses the rest of the universe. It's a question of access. Blithely asserting that "factories and data centres can be moved" hand waves the ENORMOUS barriers to doing so.
We can build O’Neal type colonies at the Lagrange points to have full gravity.
Why? This would be shatteringly expensive and resource intensive, requiring constant upkeep. What's the upside?
Manned space travel and colonization is key to building a post scarcity future.
Again, you aren't addressing the really enormous barriers. If these things were as simple as just saying them, I would agree with you. No one yet has come up with a remotely feasible plan.
Spending that money here will never fix things. The planet has finite resources and room and it is clear that the massive amounts of social spending has not moved the needle at all.
See first point, above. Massive amounts of social spending have, in fact, "moved the needle" in many, many measurable ways. For example, most women no longer need to be terrified of eventually dying in childbirth. They can even go to school, have jobs and get paid. Your risk of dying vilently is a fraction of what it was in Shakespeare's time. You aren't nearly as likely to be trapped in your social class from birth. etc.
But let's assume that you are right, and "spending that money here will never fix things." What makes you think spending it on astronomically more expensive things in space will help?
Like, if I can't afford health care right now, why would I want untold trillions of tax dollars spent building and then maintaining "O’Neal type colonies at the Lagrange points"?
I agree that science for its own sake is worth investment, within reason. But many of the ideas being floated strike me as distinctly pollyanna-ish.