A fascinating and depressing piece by Daniel Gordis. Read the whole thing, but here's one important point:
Many people are put off by the Israeli national affect, which they take to be a mix of arrogance and bravado. This is a misperception of an attitude that is born, in truth, out of collective relief: We Jews no longer live--and die--at the whim of others. That sense of security would evaporate the minute Iran had the weapon it seeks. Even if Israel does possess a second-strike capability, and even if the U.S. could be counted on to punish a nuclear attack on the Jewish state, the existential condition of the Jews would still have reverted to that experienced in pre-state Europe. It would mean that Jews by the tens of thousands could die because someone else determined that it was time for them to do so. No action that Israel could take in response would change that fundamental reality.