I personally think that Iran's leaders would be dumb to attack Israel with its nuclear weapon. And since the US will never allow Israel to get attacked by Iran, such a scenario results in their cities being flattened. So saying Iran will do that is simply fearmongering.
This is something that I have been thinking about. The Ayatollahs have been in power for 36 years now. You don't rule that long possessing the sort of suicidal stupidity needed to try to bomb Israel. I really doubt that Iran would actually nuke anyone.
Furthermore the regime is under increasing pressure domestically and when you consider the new threats Shia face in the rise of Sunni extremism, the last thing Iran needs right now is to be starting nuclear wars. While this type of illogical diplomacy could
maybe be expected from an entirely rouge state like North Korea, but even in that case, the Kim family has a vested interest in self-preservation as well.