I don't think anyone's saying that.
If Iran got nukes, it could attack us anywhere it wanted. Or our allies. A rowboat in the Hudson River would be all it takes. Really, this isn't a country that thinks in terms of its own self-interest, which makes outrageous acts of aggression completely within the realm of possibility. We're talking about a rogue state with explicit goals to acquire nuclear technology. That alone is enough to make us worry. The Saudis and the Israelis have been pushing us to act harder even when Bush was president.