Well, unless you've killed 10+ innocent people, I don't think there's a way to prove it, nor do I think you should be so sure of yourself.

Beyond people having problems killing others, the nature of the job in question is that you will have visuals on people you are responsible for terminating, and there will be mistakes made, often on Intel you've provided ("it looked like a terrorist meeting to me, how was I to tell it was guys shooting the shit around a campfire?")

I used to think of myself how I think you think of yourself, where I thought I could view killing and death rationally. Since then I've had a few points where I had to deal with the death of people I knew and while I was somewhat clinically detached most the time, there were instances, sometimes months later, where I was overcome with emotion for the first time regarding that incident. There's a fine line between being able to rationalize your decisions and being in denial, and the human mind doesn't always act as you want or expect. And besides making people accidental murderers, how do you test for this? Seems like many people in the army would probably identify just as you are, yet we still have this problem.