Humans cost too much in the space frontier . . . better machine technology in space than humans! The Big Lie since without human growth momentum to the space frontier the cost of human growth / human stagnation / human shrinkage on Earth is growing untenable. The cost of humans on Earth, period, is growing insupportable. The path to dark ages is not too many humans but too few . . . population die off, population infertility, population energy, loss of mass genius -- which Will Durant ('The Story of Civilization') said always comes from the ranks of the common people, the peasant population, the would-be frontier population, and never from the elites rigidly married to a steady-state elite status quo (the cost of which inexorably rises to infinity (amply exampled in Aldous Huxley's, 'A Brave New World')).
So, we have an increasingly closed system of Earth only as the space economy shrinks (as permissible human space participation over time shrinks and costs more and more , , , and the cost of humans, and human civilization (energetic infrastructure) on Earth, period, is increasingly -- inexorably -- untenably rising.
Hawking's 1,000 year prophesy to human downfall without birth to space frontier from Earth was wildly, outlandishly, optimistic as to time. We need to begin transferring industry and economy to space fronter, building in space -- especially spin-gravity stations, tooling up to space colony facilitation for life -- now, not later (and later, and later, and later. and.... costing too much; too far too much; too far, far, too much; to infinity), Things won't hold. Won't sit still. Won't wait til later, "when costs go down" (hahahaha).
What of the Old-World Earth while things are moving, gaining momentum, in and to the New World of Space Age Frontier? You'd have to be blind to history and physics to not see that then the Old World -- the homeland world of Earth -- would itself be a New World Frontier from being a big part of it! In 1512CE, Sir Thomas More wrote 'Utopia' as a nostalgia for the Middle Ages because he hated what the opening systemic New Frontier Renaissance Age (to maritime East and West) was doing to his elite human feudal fiefdom of Old-World Europe.