This is getting uncomfortably political. I can tell because I think you misunderstood what I said, and everytime I try to reply, I feel like I'm misinterpreting your viewpoint as well. Yuck. (The Heinlein I meant to reference was "Red Planet" - Mars is controlled by the "absentee landlords" of some earth-based corporation, interested only in mining. People living on mars are there by contract, and have no proper elected representation.)
Going backwards to shoot the low-flying birds. I don't care if SpaceX gets a monopoly - the free market is very good at some things, but human rights etc. are not on the list. And I don't forsee any danger from SpaceX to earth-dweller - I fear what space exploration will be if going to space means contracting with - and giving up various freedoms to - one of maybe 6 large space companies. NDAs? Less benign forms of censorship? It's not a pretty picture, in my mind.
> ALL organizations are corruptible; the U.S. government even more than SpaceX.
Define "corrupt". If you mean "doing things for money", then SpaceX, as a company, is inherently more corrupt. If you mean "straying from the core purpose", then I view SpaceX's uncorruptibility as a bad thing, since the core purpose of any corporation is the morally ambivalent "make money" - at least democratic governments have an attractive baseline.
Now for the hard bit to explain. To my mind, no power structure is benign. Any concentration of power is inherently dangerous, and needs to be checked by other power structures to maintain some sort of equilibrium. I think we can agree on this. The difference between our government and a corporation is that our government was set up with the explicit purpose of being properly fragmented to balance itself. It's in bad need of adjustment nowadays, but along with most other democratic governments in the modern world, it's worked pretty well. Democratic governments tend not to massacre civilians, tend to be internally peaceful, tend not to declare war on each other, and tend to care a lot about scientific progress. Despite all the mars (no pun intended), it's a pretty good track record.
Companies, on the other hand, have no such internal mechanisms for self-regulation. Their role in society is efficient resource allocation - and they're damn good at that! - but nothing more. I feel like libertarians (and others with similar views less fond of labels) want to claim that because there's competition in a free market, there are adequate "checks and balances" - but if all powerful entities are pulling in roughly the same direction, it doesn't matter how many there are. The free market was not designed to protect human rights. It was designed to allocate resources for some externally set (via regulation) good. It does that very well, but I don't think we should mistake that for it being "good" in a broader sense. For that, government's still the best thing we have.
Back to space. As things stand right now, I don't see governments being able to project any sort of guidance to push corporations towards some common, ethical good. The free market won't (I think) move in that direction on its own. And so we're left with "absentee landlords".
And now I'm afraid I explained it wrong. Ugh.
Shorter, possibly better summary: corporations are good for one thing (efficient allocation of resouces). Governments are good for another (high-level imposition of some broad purpose on human events). Neither necessarily has purely good intentions, but democratic governments are more likely to lean that way, because of their design. So I want them to have certain powers, to help push society towards respecting human rights blah blah blah.