That we have the "luxury" of toying with such notions is a feature of how detached we've become from the reality of war. Since the Civil War, the US population has not really experienced it first hand. WWII was remote. This "disconect" explains to me our willingness to use war readily as an instrument of policy. They always happen "over there" somewhere. Nuclear war will wake people up quickly enough. That will be a little late, but we are a species full of hindsight. No need to "do what it takes." We will be ashes in the short run. So will "they." Both sides will have hit exactly that level of total destruction which you have astutely pointed out.
As long as the peripheral wars continue to happen "over there somewhere," we will have plenty of stomach for war. And we will be able to argue such frivolities as you've mentioned in as detached a manner as we discuss a TV show.
So...Yes, we don't really have the stomach for it, and No, we "don't need" the stomach for it, now...do we?
I remember being told at one time that (I may be paraphrasing here) according to Sun Tzu and his Art of War, that to win a war, you not only have to defeat your enemy militarily, but also change his willingness to wage war. If we look back in history, this has been the almost total destruction not only of the military elements but also the political, economic, and, unfortunately, large parts of the population supporting said enemy. This is where the US and it's allies I believe are no longer willing to go. When you argue, as an example, whether a US Citizen that is a confirmed enemy combatant should be captured and put on trial, or killed by a drone strike, then you really need to ask if you are willing to do what it takes to win said war.