You do the job you are paid to do. That is the "mercenary ethic" that just happens to be *gasp* the same as Joe the Plumbers "work ethic." Some people are paid to provide violence. Either for actual fighting or to be available for actual fighting. You can call it "security contracting" if you want, but in the end it is paid violence. This says nothing about whether the cause for violence is noble or altruistic. The old saying, "Football players and whores are in the same business, ruining their bodies for other peoples benefit" runs true for Soldiers of all stripes (and fortunes).
But this brings us back to the topic of killing. It takes a certain type of person who can kill for a paycheck. Someone who can turn off the human empathy that he or she would feel towards the victim and yet not become the psychopath that the Brady Bunch believes all gun owners to be. Joan Peterson likes to say that all gun owners are people on the edge ready to snap without warning. This couldn't be further from the truth. Very few people have the capacity to kill without first being threatened.
Most people have no problem with the use of force for self defense. What most people are squeamish about is killing for reasons OTHER than self defense. Rudyard Kipling's "The Jungle Book" boiled down the ethics of the jungle, "kill or be killed, eat or be eaten" which sums up generations of Western ethics on violence. So when it is your job to kill for a paycheck, you are just another jungle predator killing to eat. It isn't romantic, it isn't honorable, it just is what it is. And I see little difference between those who sign a contract and wear a uniform and those who just sign a contract. Serving under color of law is all fine and dandy until some illiterate tribesmen with a handicam beheads you to the sound of stirring music.
I've always tried to not BS myself and tell me that I'm doing things for some noble cause or some such. I do keep a list of people in my head who are worth dieing for, but lately my service has felt less like service to them and more like work for an administration bent on giving the UN a lease with option to buy on the US Military for a global "peacekeeping" force. There will always be people worth dieing for and killing for, but noble causes are few and far between.
I've had to take a long navel gaze over the years and ask myself I can kill to earn a paycheck and if I can live with myself afterward. I'm still here so the answer seems to be yes. A man I respect told me, "When you wake up three days in a row feeling like you can't make a difference in a fellow Soldiers life it is time to get out." So far that hasn't happened to me yet and I hope that it never does. But when it does, it will mean that I have somehow disconnected from an organization that I have invested in, and that is a clear sign to let go.