I strongly disagree with that notion, nobody is prepared to die for money, there needs to be a superior purpose that a soldier respects and offers his life to protect. If someone promises you a lucrative sum to dance with death, I bet you wouldn't take it and neither would the soldier, they are after all, humans with feelings and families. Even if the govt tried to push the into it, they would simply rebel against the govt. There is a lot of honour attached with serving for the UN and soldiers feel proud representing their country in a foreign land. Then obviously, if you have a mess of state with failed state machinery, you need to borrow the state machinery from others to uphold order,that's just what the UN is for.