Why is it assumed that Iran would not be deterred by Israel’s nuclear strength? The answer I hear most often is that Iranians are fanatics and wouldn’t hesitate to commit national suicide if it could get at Israel’s throat.
Iran is a very calculating and rational society, just as the Soviet Union was during the Cold War. Deterrence worked then. Only a wild fringe advocated a pre-emptive attack on Russia back then.
And why do we think Iran would give a bomb to terrorists if it had one? Nations sometimes use terrorists for their purposes, although they call them freedom fighters. But why would Iran give Hezbollah an atomic bomb any more than we would have similarly armed the Contras in Nicaragua? Such groups are too undisciplined.