A general policy of "If you want it bad enough, we'll give it to you" has major costs, actually. In the short term, yes, you're avoiding the loss of lives. Long term, though, everyone knows that you'll give in if they threaten you hard enough, so you incur on many costs or loss of potential benefits.
You think Argentina is going to come and try to occupy Cornwall?
No, not Argentina. Key word is "everyone", as in, y'know, everyone who might want to demand something from the British government. It doesn't even have to be land, could be policy reform or money or whatever. If you have the general policy of avoiding any confrontation when the threat of violence is high enough, then anyone who can create a large enough threat of violence wins by default, even if
actually doing what they threaten to do would be even worse for them.