I think we need to be specific about scenarios here. For example, right now we don't need to worry about extremely high speeds, so defending against inbound objects should be fairly easy. I think for the near future, (US, Russian, and Chinese) interceptor missile technology will outpace abuse-of-spaceships technology, so once there are a bunch of spaceships flying around and/or mining operations get started, it may be easiest to just keep track of relevant objects and shoot them down. I think that should be more than enough, since I just don't think there are very many people who'd want to use spaceships as makeshift weapons who don't have access to better weapons already. If we make it to the far future (where we might expect significant-fraction-of-c speed ships) without singularity things happening for some reason, on the other hand, more authoritarian external control may become necessary.
A reality of physics, and one that doesn't get much play in science fiction, is that as soon as humanity gains space travel, anyone in the asteroid mining or space travel business will have city-busting capabilities at their fingertips.
It's there in classic sci-fi, but not so much recently.
This discussion was started in the comments to:
http://lesswrong.com/lw/gln/a_brief_history_of_ethically_concerned_scientists/
In the "Ethically Concerned Scientists" post, Izeinwinter commented:
A great start to a discussion here.
You've considered people going loons and some general security, but it would then become a hacker war along the lines of who could break the security and gain control of the space ships.
It doesn't address the problem of the leaders using the ships as threat weapons, since they have legitimate control, but can still make terrorist decisions.
And I'm terrified of your idea of turning spaceflight, which I see as the ultimate freedom, along the lines of Niven's Belters, into a state-controlled affair like the Soviet navy with political officers.
Now, one thing I think is a useful safety control that doesn't lead to worse problems is the destruct option. All major rockets have them right now, since if it goes out of control it's a huge hazard for a great distance. And although I don't like the idea of all personal spaceships being under a safety officers thumb, it might be better than the alternative of terrorist groups gaining control of asteroid mines and holding the world hostage.
You're right about great story potential though, in any of these scenarios.