The thinking is it is easier to dissociate consequences when they are nothing but pixels. It become more of a video game than a reality when sitting in a safe gaming pod flying the drone. It isn't fully transformed to a game, but it is to an extent.
Compare internet forums vs f2f discussion - it is much easier to end up in a flamewar saying hurtful things on the internet when your opponents are faceless words on a screen than when it's a person sitting across from you.
Look, I don't have a position in this discussion, but your argument is prototypical for much of the others in this thread and it just seems so flimsy. Here is another totally made up argument just the other way around: for a UAV pilot, and their commanders, the 'kill order' is much more rational. Soldiers get to make decisions that are not influenced by the hate against the person who 2 minutes ago shot their buddy next to them in the head. Nanking massacre? Would never happen with drone pilots.
See? I'm not saying that argument is right. It is only just as neat, simple and (probably) wrong as the 'killing through a joystick causes more casualties because it dehumanzes the process' argument.
Compare internet forums vs f2f discussion - it is much easier to end up in a flamewar saying hurtful things on the internet when your opponents are faceless words on a screen than when it's a person sitting across from you.