You miss the point. The Iranians want Mecca as it is, intact with no blemishes.
Mecca is the most holy of hollies and the reason for being Moslem.
Never in their wildest dreams would the y consider harming, much less destroying the site of the pilgrimage
They have no logic nor reason, I bet that in their beliefs any method possible to defeat the enemy, does that truly protect Mecca?
I was reading how the British during WW2 knew a bombing raid was going to happen upon Coventry, but if they took action to defend it they would lose their intel, so they held back, and Coventry was destroyed.