I used to think this is a good idea. However, the reality is when you join the military it should be reasonable assumption you are going to be sent somewhere to actually fight at some point.

My proposed alternative would be, when you sign up for the military, you are presented with a list of "regions" in which you are willing to be deployed in a combat role, with pay/benefits scaling accordingly the more regions (and more "in demand" regions) you are willing to be deployed. So you could potentially ahve a group that would not fight in the Middle East but would fight in the Pacific, etc. Of course you can't have too many declining service in too many reasons, but if it starts to get expensive to find recruits willing to fight in a given region thats a clear sign somethings amiss with popular sentiment.