Why is this easier to see than the same conundrum on the international stage? When a nation starts a war to effect a "regime change," it is engaging in murder on a massive scale. The morality, if anything, can only be worse than killing one's neighbor to prevent an alleged crime-to-be.
Am I afraid of people who mean the U.S. harm? Sure I am. Am I happy about living in a state of fear? Of course not. Do I therefore support blasting at every scary looking person in the world who gives Americans the evil eye? No. That policy is not only immoral, it will achieve the exact opposite of greater security for our children. Either reason on its own is enough for any sane person to reject such a course of action.
Though of course one could overcome libertarian objections by a few simple steps.
1)Privatize the 82nd Airborne.
2)Find an Iraqi property owner to invite the 82nd Airborne onto his land. Or find some unowned (government owned) land in Iraq and homestead it with the 82nd Airborne.
3)Wait for the government of Iraq to "initiate the illegitimate use of force".
4)Blow 'em away.
All perfectly legal in libertarian terms.
BTW, in Afghanistan we were invited in by (one of) the government(s) of the country -- the Northern Alliance. Maybe someone in Northern Alliance territory even invited us in in his private capacity.