I think the whole "Iranian Nukes" debate and question might benefit from a historical review of a parallel issue..
There was a time when the United States could have stopped the Soviet Union from building Atomic weapons (not from learning about them - they stole German scientists just like we did).
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And this is the analogous situation with Israel and Iran. It isn't a perfect parallel, but it is instructive. Kruschev stood at the Untied Nations, slammed his shoe on the podium and shouted that the USSR would bury the United States. The stated goal of the Communist System (printed in he manifesto and repeated constantly) was the violent overthrow of the capitalistic system in general and the United States in particular. And yet we never preemptively stopped either the USSR or China from obtaining these weapons.
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So why are we thinking of doing this in the case of Iran. Or why is Israel all but stated they plan to proactively attack Iran to prevent them from getting these weapons? This sort of preventive action ONLY makes sense if it is 100% effective and a surprise and we are convinced that Iran will act in a non-logical way. Any reasonable state actor would not use nuclear weapons against a nuclear state with a counter-strike capability. And Israel has loudly proclaimed it's submarine based counter-strike weapons and it's hair trigger response.
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Assuming Iran is a realistic state actor, then a US/Israeli first strike would make sense only if we assume that Iran planned to give the weapons to a non-state actor (like Hamas or Hezbulla). But why would they do that? In our historical parallel, neither the USSR nor the USA gave these weapons to non-state actors, even as we fought proxy wars around the world. Boht countries understood and stated that a nuclear attack from a proxy is tantemount to a nuclear act from the supportive country.
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To say Iran doesn't understand this same equation is simplistic. Iran already holds back its more sophisticated and effective weapons from Hamas and Hezbulla - why would they suddenly cough up nukes?
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Perhaps it makes sense to strike Iran with enough force and in enough places to delay their nuclear weapons capability. But it will cause a massive death count of civillians and be the very act of war that Israel is worried about. I think more explanation and thought is needed here.