You have three unsupported assumption:
1) That the Iranian are actively building one ( I think they might be, but no proof on that. However, they might want one but this is a different issue )
2) That they will use it
3) Iran is not a rational player( goes hand in hand with 2) )
Iranian actions since 1979 are reactionary actions ( they are scared from being invaded by the US ), an Iranian bomb would serve the role as an invasion inhibitory weapon. However, if you are going to quote Iranian officials saying that they will erase Israel from the map, you'd be a fool if you do not place it as verbal showcasing intended as something to gather support from Arabic populations. The matter of fact is on the long run Saudi Arabia has been the prime motivator and money supplier of every salafi/Wahabi Jihadist in the world. Yet we turn an eye on their actions because they are our allies ( I wonder why! --wink wink oil--).
Iran and Saudi Arabia are both terrorist loving countries, both are bad. It is just that one is much more effective at what they do. And I would love nothing than see a regime change in both of these countries.
I guess in the end we are both agreeing to how bad these two countries are, just differing on who is worse. I think in parallel to imposing sanctions on Iran, Saudi Arabia should get its own version of Oil embargo.
