Why assume that only a government can enforce property rights? Even though we've been conditioned to think that only governments can perform this function, this idea is far from obvious and, I believe, it's outright erroneous.
There has been a long tradition of social/economic thought exploring the idea of private production of security, dating back at least to de Molinari's seminal 1849 article “De la production de la sécurité,” in Journal des Economistes. More recently, it's been pursued by Hans Herman Hoppe in his The Private Production of Defense.
Everywhere we look, it is precisely governments that wreak havoc in the lives of people on massive scales. E.g., WWI and WWII would've been impossible to pull off by the private sector. Going to space offers humanity a chance to implement alternative ways of living for those who want something else. Let's not assume away such a precious opportunity.