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.
Naturally; you are essentially without a rational reply. The point, which I made adroitly by mentioning "phasers", is that you're postulating a world in which the US has undergone a libertarian revolution, but in which nothing else has changed, including the other nations' governments, their policies toward the United States, their technology... nothing. You are also postulating that the dissolution of the military included the utter disappearance of all classified technology, which is on the face of it absurd. To consider this hypothetical even somewhat realistically, you must also consider at the very least the following:
The impact of massive declassification of unknown technologies, including but not limited to: powerful spy satellites; highly effective launch technologies; advanced aerospace technology; advanced encryption; etc.
The impact on other nations' policy of the US dissolving its expeditionary forces and withdrawing unilaterally from Germany, South Korea, Afghanistan, Iraq, Mogadishu, and every other darn place,
The impact on other nations' policies of sudden unrestricted free trade with the United States,
The disposition of the existing US nuclear arsenal and other military assets,
The effect of arming the entire populace of the US with (at least) small arms, and
The ready availability of, say, howitzers on the open market in the US.
When you say, with no preamble, "What about when China attacks?" You're assuming that the Libertarian Bloodless Coup had no effect whatsoever on the world stage except the demobilization of US armed forces. That isn't even vaguely realistic.
The examples with which I countered are, of course, wildly hypothetical, but they should at least jog you to a realization that many things would be different in this hypothetical scenario.