Actually, my own sources tell me that, though many Israelis take seriously this prospect of Iran trying to annihilate them, Israel's policy elites by and large don't. They realize that Iranian leaders aren't suicidal and so wouldn't launch a nuclear strike against a country with at least 100 nukes. On close reading, as others have noted, the Atlantic piece [Jeffrey Goldberg's] suggests that this sober view indeed prevails in Israel's higher echelons. Though Netanyahu warns us about a "messianic apocalyptic cult" possessing nuclear weapons, he doesn't seem to be seriously imagining the "cult" launching a first strike. Goldberg writes: "The challenges posed by a nuclear Iran are more subtle than a direct attack, Netanyahu told me."
So what are those challenges? For one thing, "Iran's militant proxies would be able to fire rockets and engage in other terror activities while enjoying a nuclear umbrella." Whether heading off this prospect would justify bombing Iran is an interesting question, but we don't need to ask it, because the prospect isn't real. There's no way Iran's having a nuclear weapon would keep Israel from taking out Hezbollah missile sites in Lebanon as missiles from them rained down on Tel Aviv. If the Holocaust has left Israelis with an exaggerated fear of Iran's intentions, it has also left them with an absolute refusal to be cowed.
It stands to reason: if the Iranians aren't suicidal enough to risk a massive retaliatory nuclear strike by Israel, then Iran's 'militant proxies', like Hizbollah, won't have a nuclear umbrella. So, as I've pointed out before, the distinction between a direct Iranian nuclear threat against Israel and the 'more subtle' challenge isn't well made.