Their isn't going to be any time for ignoring reality or anyone coming to their senses once the 1st nuke goes off. The response triggers will be pulled without any time for PC to interfere and the end result will be the end of Islam and a large part of the rest of the world. The war on terror will have been won at a price that should never have been paid. There is still the chance we shall be the trigger pullers and I relish the thought of Mecca being turned into glass before a civilized city has to be sacrificed.
Your scenario is more applicable to the days of the Cold War, when you knew exactly where missile launches came from. Unfortunately, with our current adversary, it isn't that black and white. Who do we strike out against? Do we take out countries where the terrorists may have originated from, even though the Government an erst-while ally (e.g., Pakistan and Saudi Arabia)?
Your assertion that we just take our Mecca isn't realistic. Responses aren't just blind spasms, they are based on war plans (existing or to be developed). Somehow I doubt that there are war plans that include the automatic destruction of Mecca before a lot of the Whos get answered after an attack.
My point in all this is that it took us about a month to respond in Afghanistan after 911. I think it will probably take 2-3 weeks to respond appropriately after a nuke attack. During that period, you're going to have every major newspaper, TV channel (sans Fox), and many Democratic politicians calling for "restraint". It will be very hard in that environment to respond with nukes.