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It totally obliterates one of their pillars of their faith, making it obvious that the religion is not backed by God, since God did not protect it and they are only left with 4 pillars unless they want to glow in the dark.
Nuking Mecca does a lot in the fight against islam, not only does it let muslims know their religion is false it plainly puts forward that they are toast if they mess with the West. It is what has happened over and over throughout history when islam is on the march and the West or others have put a stop to its march.....something so horrific is done that it scares the living daylights out of them thus stopping the march for a century or so until it is forgotten.
The only problem I see is in believing that the State Department or any part of the US government has the gumption to go through with this plan.....FAT CHANCE.
Wanna make a bet?