If your neighbor down the street has sworn to kill both you and the Goldsteins next door - just as soon as he can get his hands on a gun - should you wait until he actually aquires that weapon, kills your friends, and starts firing bullets into your home before you take action?
If your neighbor threatens you (note to self: Iran has not threatened the US...if Israel wants to attack them, let them suffer the consequences) and you attack and kill him, you appropriately get convicted for murder.
If and when Iran attacks us, we are justified in retaliating.
An attack on Iran would inflame the entire region, fail in its military and political objectives (we have zero ability to "invade and subdue" Iran), and further turn the rest of the world actively against us. It would be 180 degrees against our own interests; an act of supreme shortsighted stupidity. But then again, so was the invasion of Iraq, which you also vehemently support. After being so wrong for so many years, and supporting such complete fucking buffoons, one would think that you, too, would come to this more adult, pragmatic, global, and longer term viewpoint. So far, no good. Your unquenchable need to play the contrarian and distaste for the mythical enemy of 'liberalism' outweighs such an outcome.