Methinks you’re confusing rational with responsibility, a mistake that Giuliani and a bunch of Republicans make.
Although U.S. attacks on and intervention in the Middle East is the rational for (and in that sense only the cause of) the 9/11 attacks, only the people who actually planned and committed the attacks are responsible for the lives lost, because they had the free will to choose not to kill innocent people but chose to do so anyway.
Although the U.S. becoming independent was the rational for (and in that sense only the cause of) the British war against the United States, only the peple who actually planned and committed the attacks are responsible for the lives lost, because they had the free will to choose not to kill innocent people but chose to do so anyway.
Whether an entity employing force is a “voluntary association” or not is irrelevant. The KKK was a voluntary association insofar as no one was forced to join it, but that does not mean there was anything immoral or unjust about fighting back against an attack by the KKK. What’s relevant is whether or not the non-aggression axiom has been violated.
This is why Rothbard goes over in great detail contracts in his The Ethics of Liberty (and why I believe Dr. Walter Block is wholly incorrect in his opinion that voluntary slave contracts can be enforced). Any contract that one signs saying that one will remain within an association forever or even for a given length of time is not enforceable with violence.
Let’s say I sign a contract saying that I will be your slave for five years, at the end of which I shall be freed and you shall give me $100. Let’s say I choose to break off the contract three years in. Would you be able to force me to remain your slave for another two years? Absolutely not! You would have no right to lay even one finger on me. But, likewise, I will have no claim to any portion of that $100. If I make it through the full five years, it would be your obligation to pay me the $100.
In essence, since a person can leave such a contract at any time and for any reason, the notion of voluntary slavery can be seen for the oxymoron it is. The instance above is not slavery, and cannot ever truly be slavery, because it is not enforceable with violence. Slavery is an institution which, by definition, is enforced with violence or the threat thereof. Throughout the entire five years, I’m free to walk away from the arrangement, gaining for myself the complete and total rights I had previously (and therefore all along).
If a voluntary association decides to fight me for leaving it, it is therefore not defending itself, but rather aggressing against me. I have every right to defend myself.