The world would conceivably br laid to waste if we just up and nuke Mecca.
There IS a domino effect:
We nuke Mecca
Iran nukes Israel
Israel nukes Iran
We nuke Iran
Pakistan nukes India
India nukes Pakistan
China nukes both of them
We nuke China
N. Korea nukes Japan and S. Korea
We nuke N. Korea
Iran nukes Western Europe
And we all fall down...