So there's lots of fuss about how Iran is pursuing development of a nuclear industry, whether it's for the purpose of generating electricity, manufacturing helium and medical radionuclides, manufacturing specialty anti-armor weapons (i.e., depleted uranium shells) or for the purpose of building nuclear weaponry.
There's talk, in the USA and in Israel, possibly in other allied countries, of attacking Iran to halt their progress in refining fuel and doing interesting things with it, whatever those things might be, lest it turn out to be manufacturing nuclear bombs to be used against Israel, ships in the Persian Gulf, whatever.
For many reasons, this would be a bad idea. It's logistically difficult, which raises the likelihood of things going horribly wrong for the attacking force. It's difficult in terms of applying force, because as I understand it, the targets are distributed and well-protected. Plus, Iran has a reasonably well-armed conventional (non-nuclear) military and is strategically placed to retaliate by cutting off shipping through the Gulf. Deliberately provoking them by attacking targets on their soil is essentially asking for a war to break out. You'd have to be stupid, delusional, or flat-out evil.
But here's another thing to consider: Iran is not a nuclear menace to Israel or the USA or Russia or anyone else, really, since nuclear powers don't use nuclear weapons in first strikes.
The fact is, there is no way to "win" a nuclear war. Even an exchange of single warheads would be devastating to both states, much more so for an exchange of a few dozen. Of course, keep in mind that I am not a nuclear strategist, nor do I play one on TV...
No rational actor would launch or otherwise deploy a nuclear weapon in a first strike, now that there are multiple nuclear powers, because this invites nuclear-armed retaliation either from the target state or from its allies (whether or not the target state has nuclear weapons of its own).
I can't state for sure whether it's true or not, but legend has it that during the 1973 war, Israeli high command authorized the activation of Israel's nuclear arsenal. No such shot was fired, of course (we'd know about it) - why? Because it makes people so goddamn angry at you when you nuke them or their friends, you'll bring hell down on your own head for it. Possibly in a very literal fashion, if a nuclear-armed ally (e.g., the USSR) were to retaliate in kind.
We also know that those dear mutual friends India and Pakistan have fought against each other a number of times, including after both developed nuclear arsenals of their own. They haven't used these weapons on one another, though - why? Because it invites retaliation. Besides, neither side can be sure that its first strike would destroy its enemy's ability to retaliate.
It's all about mutually assured destruction.
So the Israelis are afraid of an Iranian nuclear strike against them? Keep in mind that the Israeli military, while not exactly world-class, is pretty impressive compared to the armed forces of nearby nations. Thanks, no doubt, to a generous helping of military aid from various NATO members and probably other states as well. Consider the following scenario:
1) Iranian high command authorizes the release of multiple weapons from its (hypothetical) nuclear arsenal against Israel. Nuclear bombs strike Israeli military installations as well as cities of political or economic value, such as Jerusalem, Tel Aviv, Haifa, Eilat, etc.
2) Needless to say, the Israeli state is devastated by the attack. Millions are dead. Vast areas are radioactive wasteland. Surviving members of the chain of command are not going to be positively disposed to whoever done it to them. There is a non-zero likelihood that the first strike has failed to destroy all Israeli ground-based nuclear attack platforms (missiles or aircraft); in addition, submarines at sea, which may carry nuclear-armed missiles, will likely have escaped.
3) Israel, via any or all means at its disposal, launches a nuclear counterattack toward Iran.
4) Iran gets pasted. Not destroyed, but badly hurt. Millions dead, cities and sites of economic, military or political importance vaporized or rendered uninhabitable.
Another -
1) Iranian command authorizes the release of nuclear weapons against shipping in the Gulf and/or American naval assets in the Gulf.
2) American naval assets in the Gulf, backed up by American assets elsewhere, retaliate in kind against Iran.
3) Iran gets pasted.
And another -
1) Iranian command authorizes the distribution of nuclear weapons to non-state terrorist groups.
2) Said groups use the bombs.
3) The world reacts to those groups and Iranian sponsorship in various unpleasant ways.
4) Iran gets pasted.
They don't want that. No sane person wants that for their country. In the age of mutually assured destruction, a nuclear attack is a last-ditch defense, or even just a poison pill for use after the last ditch has been crossed.
Note I say "no sane person". I'm assuming, for purposes of this argument, that the Iranian leadership is, in fact, sane (as opposed to gripped by religious delusions or frothing hatred). But to be honest, there isn't much reason that I've seen to assume they aren't perfectly sane and rational, so all involved should assume they are. The military, economic and especially human costs of assuming otherwise are too high.