Travis sums it up way better than I can.
Mecca IS Islam, in a way it is difficult for Westerners to comprehend. Two of the "five pillars of Islam" are based on worshipping that black moon-god rock called Al-Hajarul Aswad in Arabic. (5x daily prayer to the moon-rock, and the Haj or pilgrimage to visit and worship the moon-rock in person.) Muslims see the black stone not as symbolic, but as a physical manifestation of Allah on earth, a chunk of Allah fallen to earth. The black stone has the power to suck all of the sins and evil out of men performing the Hajj pilgrimage. (Interesting to note that Islam’s holy of holies is packed with all of the sins of all of the Muslims who ever made the Hajj.)
Devout Muslims believe that the black stone represents all of Allah's power and glory. They believe, sincerely, that if the USA launched rockets at Mecca, Allah would swat them away like flies, or turn them around to hit New York or Washington.
If Allah could not stop the”infidel” bombs, and Mecca was turned into a crater, this would constitute absolute proof that Muhammed was a fraud and a liar, and that the moon-god rock had no power after all.
This would mean the end of the entire cult of Islam. Their cult could not adapt to or respond to or overcome complete, visible proof that Allah was powerless to stop the infidel weapons.
Then you, as a westerner, should be careful about predicting how moslems would react.
Devout Muslims believe that the black stone represents all of Allah's power and glory. They believe, sincerely, that if the USA launched rockets at Mecca, Allah would swat them away like flies, or turn them around to hit New York or Washington.
Alright, let's assume that is true. That moslems truly believe that if the US launched rockets at Mecca, Allah would swat them away like flies. I don't for a moment believe that all moslems believe that, but its your hypothesis, so we'll accept it as true for a moment. Just keep that in mind. You're a moslem, and know to the very core of your being that the stone cannot be destroyed. Unfortuantely, that leads to some conclusions that don't help the case for nuking Mecca.
First, a threat to nuke Mecca would have no deterrent effect at all because they don't believe it could happen. If anything, a U.S. attempt to nuke Mecca would necessarily lead to the ultimate glory of Allah, because the rockets would be pushed away for all the world to see. The threat has no deterrent value because all moslems believe it is impossible to nuke the city and/or stone anyway.
So given the lack of deterrent effect, maybe you want to argue that forgetting deterrence, it still would result in the end of the religion because the stone would be destroyed, proving that Allah lacks power. But the stone can't be destroyed, remember?
That's the flaw in the logic predicting the demise of islam if you desroy the stone -- you can't ever prove the stone was actually destroyed. You said it yourself -- they believe it can't be destroyed. And if that's what they believe, its easy enough to craft an explanation that it isn't destroyed despite the nuking of the city.
Think about it. If we nuke Mecca, nobody can go there to look for the stone, can they? So the imams likely will conclude that the stone is still there, undamaged under all the slag. I mean, it has to be still there because it can't be destroyed. Right?
Or maybe they claim that the hand of Allah came down and took the stone away just before the missiles hit. It is now in his hands, and he took it from them because his people did not follow his commands to spread islam and destroy the infidels. They sinned by not following his law. And that he will not return the stone until his people kill off all the infidels. Maybe the variation is that he permitted the nuking of Mecca so that his people could not approach the stone (still there, undamaged) because they have sinned.
We've seen similar things in religion throughout history. Someone predicts Jesus will return at a specific time and place, or that some miracle will occur to prove something to everyone. And when Jesus doesn't make his designated appearance, or the miracle doesn't occur, the prophet then claims that there was some intervening cause or reason, and just twists that to his purpose anyway so you'll send him more money.
I came up with two perfectly valid explanations moslems clerics could make, and that's just me sitting here. I'm sure they could do better. And more likely than not, twist the nuking of Mecca into a sign from Allah that they've sinned, and need to kill the infidels to expiate those sins.
Not to mention that this chunk of Allah fallen to earth apparently already has been stolen and broken, and is now held together only with a silver band and nails. Yet, Islam apparently survived this obvious demonstration that the Stone can be damaged.