It's not personal, it's just business. WTF does this mean?

I hear this a lot, but it makes no sense to me. How is anything anyone does not personal? Every choice we make is personal. Can people really compartmentalize their psyches so much that they really believe what they do for money has no bearing on who they are as a person? If someone does something, for instance kill someone, as a part of their job, how does that not make them personally accountable? I don’t get it.

I have considered the idea that if one does something to protect others from harm, for money, that might be a justifiable reason to do what otherwise someone would never do. But, I still can’t see how one who really believes that killing is wrong would take a job where they might have to kill another human being.

Murder of course is an extreme example. How about just kicking people out of their houses or denying someone their insurance benefits because the company you work for is a “boil on the butt of humanity”?

Please explain. And would the world be a better place if the idea that we can screw as many people as we like as long as it’s our job to do so did not exist?