What's the difference between a soldier, an assassin, and a mercenary?

Originally Posted by Aramike

That's specifically my point - it stinks to have to take a human life, but the consequences of not doing so are worse.

It takes many hours to remove the built in reluctance to take human life, unless you are an abortion doctor sworn to uphold the hypocratic oath.
Part of basic training is about breaking down the natural instinct which is built into everyone reguarding killing other human beings.