I concede that raising the stakes raises the specter of defeat, and hence calls private defense into question. There are several ways to answer you.
One, I could raise the stakes still more--as I already did earlier, anticipating this--and say, "What about Iran armed with a sun-killer bomb? What would the US military do?" The answer is, of course, that it would kiss its arse goodbye, like the rest of us.
Or two, I could observe that the Pinkertons will have nukes. After all, we're postulating that government doesn't exist in the US (but does everywhere else); that implies there will be no NRC, and hence nobody to forbid the Pinkertons' building nukes. Luckily, the Pinkertons will have a disincentive to get uppity, since Securitas and Hagana will also have some nukes. And, of course, so will Steve Ballmer and, just to keep up with the joneses, so will Larry Ellison.
Or three, I could ask exactly what motive these nations will have to nuke the US which, remember, hasn't invaded anyone since government was dissolved in the Libertarian Bloodless Coup. Like Switzerland, we would be a desirable trading partner; also like Switzerland, we would be a quiet neighbor. That being the case, your proposed nuclear threat is based on the assumption that we're dealing with a madman like Ahmedinejad or Brezhnev. Of course, we might well come to face such a madman. However, I'll point out that Russia and China will deter Ahmedinejad, since their interests do not align with his, and US trade is the main thing keeping China from starvation--especially since the 100% free trade policy after the LBC...
Your General Re Defense Division is not going to build its missile defense from scratch in a year ...
Nor is Iran going to attack in a year. The dissolution of all government after the LBC will, of course, result in a flood of classified technology hitting the open market. It will take the Chinese a while to digest it all, and meanwhile the Americans will be marketing it like crazy, as will the Japanese. Given their love-affair with technology, the Japanese would be selling personal defense force-fields within the decade; kids will be hacking their iPods to use as subspace communicators. Some weirdo at MIT will invent the phaser. In the meantime, Taiwan, Tibet and Hong Kong will all declare full statehood and independence from China, leaving the middle kingdom with its hands quite full.
The standing army raises its ugly head once again,,,
You keep developing amnesia, and forgetting that every soul in America is armed--with phasers, in fact--and will fight to the last man. If all else failed, and China nuked the crap out of the US, they'd still have to kill every breathing soul on the continent before the war was over. Which raises the question, what operational goal calls for complete extermination of your best market--the one keeping your nation from starvation? The militian obviates a standing army, precisely as the 2nd amendment intended.
only this time there's no civilian oversight beyond what the Board of Directors think
...as opposed to the amazing civilian oversight that takes place now? Thfffpt! Anything interesting going on today is classified, friend. They could tell you or me about it, but then they'd have to kill us. We oversee nothing of any significance.
Indeed it does. And since I selected my examples from the real world, and because the world whackjob index appears to be increasing rapidly, one must do more than "call into question" your idea of private defense -- one must reject it.
You keep developing amnesia, and forgetting that every soul in America is armed--with phasers, in fact--and will fight to the last man.
Aallllllrighty then. I'm outta here.