That justification is really weak in reality. It's pretty solid in theory, but it's be used and abused with premeditation for a long time.
There are politicians that want to gain more jobs in their districts to get re-elected. Their districts happen to have defense contractors as primary employers.
There are people living in those districts who like receiving paychecks while working for defense contractors.
There are the defense contractors themselves who want more military orders.
There are logistics companies who want defense contractors to have those projects and military to be always actively deployed somewhere.
There are also some members of the military brass who firmly believe that if two generations of soldiers pass without seeing large scale combat, the army's effectiveness drops. So they want wars to happen from time to time simply from purely pragmatic perspective.
I can list a lot more "groups" of Americans that want the war to go on. And I'm sure you can list them as well.
None of them want to deliberately kill people, but they sure as fuck want the bombs to continue exploding and rounds to be fired, and tanks to be used up and torn, and trucks to be blown up and replaced, and fuel to be burned, and missiles to be launched, and ready to eat meals consumed. The faster the DOD's supplies are depleted, the more new orders everyone in the supply chain scores.
(I won't even go into discussing the oil sector. And I won't go into discussing the use geo politics backed by military strength to protect business interests of the US from which US consumers benefit greatly. And I definitely won't go into the whole private contractor sector, which needs the war simply to exist.)
In short, they all want the war machine to go on, yet they don't want to deliberately kill people. Some of them don't even understand how much they benefit from the war.
But in any case, you can't have a war without death.
So saying that US doesn't intentionally kill, is simply not true. There are plenty of parties/people involved that have vested interests in the war: from giant corporation stockholders to janitors mopping floors at the factories.
But they all like to pretend like what they are doing is not connected to the outcome in some way.
That's why the whole argument about deliberately killing vs. intentionally killing is complete bullshit. And the reason it's used so often is specifically because without it, the whole system of beliefs based on "us vs. them" would collapse.
Since some Americans benefit from deaths of Iraqis, shouldn't all Americans be help responsible?
If not, then why is it OK to hold all Muslims responsible for what some of them are doing?
Terrorism is a business. Military is also a business.
So you can't have it both ways.
If you put all Muslims into one monolithic group, then you should also put all Americans into a monolithic group as well.
And if you did that, then Americans would really begin to look like a bunch of bloodthirsty gready bullies who should all be exterminated for the betterment of the world.
Sadly, that's pretty much how the US is seen from the outside.
As I've already said, I've never supported the war in Iraq and always knew it was based on bullshit. I'm well aware of how our military industrial complex operates - but if these stupid motherfuckers would stop trying to attack innocent Americans they would have more support. When they keep acting like bloodthirsty savages, it makes it much easier for the US to justify it's actions and easier to sell it to people as justified.
I guess I would point to Gandhi's approach to dealing with the British - at some point the British realized that no matter what they did - they looked like the aggressors and lost credibility. If Gandhi had lead a terroristic campaign against the British, it would have been easier for them to justify staying in India, the use of force, etc. When you use terrorism against civilians you put yourself in a situation where nobody remembers who struck first and all actions seem justifiable. You also erode support for your actual cause and put it firmly in the hands of the extremists who generally do not have the interests of the civilian population at heart.