Because of interplanetary transportation costs, due to physically unavoidable planetary gravity wells, the existence of other inhabited planets has essentially zero effect on the prosperity of the average Earth inhabitant. There is physically no way to build the space equivalent of cheap maritime shipping.
Even if we successfully build a space elevator and putting stuff on orbit becomes relatively free, we would still need to build a 100% sustainable spaceship. Or a completely game-changing technology like teleportation, and there's no proof such thing is practically possible.
It seems to me that's an achievable goal... if everyone throws risk aversion/mitigation out of the window.
No rules about nuclear power on ships, no worrying about contamination on other planets, laissez-faire attitude about risks that come with space launches/travel and fully automated control of rockets/spaceships, massive investment in life support systems and AI, etc.
