Our government has, as it says, some concrete knowledge that links the perpetrators to the Al Qaeda network. Since the government of Afghanistan won't end Al Qaeda, our government is at war with Afghanistan. It is conducting the war in a way that avoids civilian casualties, but the paramount goal is to win the war. Now, our government may be wrong on all accounts, but it has the prerogative of using its judgement as it generally has the prerogative of going about its legitimate function.
It is a valid question whether preemptive violence on foreign soil is legitimate. My view is that it is legitimate under the circumstances because given the nature of terrorism there is no other sure way to prevent future attacks. One is entitled to his defense being effective no matter the time or place of the defensive act.
If you object to national defense being a legitimate government function, then it is not libertarian, but anarchist position.
Of course we have to take this a little further retaliatory war against non-government non-perpetrators as preventive violence by a state that may be completely wrong in its actions. And all this is justified because the government is the government until its not.
This is getting absurd. Admit it. You just want to strike out at anyone. Right? Or perhaps, as you explained to tex-oma, you think that imperialism is the proper solution. Defend this position if you will. Just dont try to call it libertarian.