Why does the liberal ideology want PC wars to be fought (if a war needs to be fought)?

Liberals prefer to fight PC wars (everyone would prefer no war). A PC war is essentially when you sacrifice your troops in order to prevent collateral damage. A stray bullet is considered collateral damage and so is dropping a nuke on a populated area just to kill Osama bin Laden. Now, while this sounds all lovey and goody, a war has never been won fighting this way. So why fight a war this way?