It's symbolic anyway. They'll just keep right on with or without the rock. Won't make any difference at all.
I don't pretend to know the inner mind of the average Islamist, so I can't fully evaluate the accuracy of that statement. There is a competing school of thought that symbolism is extremely important, which is supported by the hajj and the fact that the 5-times-a-day prayer sessions involve facing Mecca.
What I do know after studying wars that involve fanatics is that if you can sufficiently shock them (either through killing a sufficient number in a sufficiently-horrific method or through destroying everything they think is sacred spectacularily), they will lose the fanaticism. Why did Japan fold after 2 nukes, while it took Allies crawling over virtually every square inch of Germany to get the Nazis to quit?