Barring a complete revolution in technology, it will always be cheaper (by several orders of magnitude) to either recycle, find and exploit an Earth-based site,

Barring a complete revolution in technology, it will always be cheaper (by several orders of magnitude) to either recycle, find and exploit an Earth-based site, use an ersatz, or simply wage a war over a resource that is deemed needed. A similar thought on space colonization: humans would rather displace/destroy another tribe and claim their land/resources before going on a dangerous venture to go and live in a less-hospitable environment.