There is a strong temptation to begin with a question that is pretty stupid, even by my standards. Why shouldn't Iran have nuclear weapons? Too easy, you say. When the president of one country expresses a desire to wipe another country off the map, the last toy he should be allowed is a thermo-nuclear device. That's obvious.

As it is. Israel may count in some eyes as the Middle East's leading villain, in a tough field, but talk of a people's extermination is no mere rhetorical gambit. You must be able to contemplate doing the deed, or contemplate the possibility that your listeners will act on your behalf. You must be able to imagine it happening. We call that insanity. We also call it incitement to genocide. We allow no excuses after the fact, or, with luck, opportunities beforehand.

It doesn't do to say that Iran's Mahmoud Ahmadinejad is a demagogue drowning in fanaticism who talks loudly, often, but never wisely. His record of sincere anti-Semitism is well-established. He does not call for Israel's destruction just to rally the hard-liners at home. He is one of them. A nuclear capability in such hands? Unthinkable.

So much for the problem; now find a solution that will work. If recent experience in neighbouring Iraq is anything to go by, the trick might be to avoid any strategy that would cause things to be worse than before. Reports coming out of Washington suggest, unbelievably, that this single lesson has failed to penetrate in and around the White House.

Iran is pressing on undaunted with its "peaceful" uranium-enrichment programme. In a fortnight the country will face international sanctions for its pains. Diplomacy, fitful and lacking coherence, has produced no obvious result. Impatient with this pussyfooting, some of the Americans want to cut to the chase: start the bombing.

Lots of people are horrified, predictably, even if some of them are not predictable opponents of American policy, or even of western power. Three former US commanders, one of them the ex-head of central command, are not often confused with doves. Writing in The Sunday Times, nevertheless, General Joseph Hoar, Lt General Robert Gard and Vice-Admiral Jack Shanahan argued that a strike against Iran's nuclear plant at Natanz, in the heart of the country, "would have disastrous consequences for security in the region, coalition forces in Iraq and would further exacerbate regional and global tensions".

The analysis is one thing. Almost as important is the fact that when retired American commanders speak out in such a way they speak, invariably, for serving brother officers who are losing the argument in Washington. The political intent, I suspect, is to restrain George Bush from attempting a spectacular distraction to the Iraq debacle. Generals know how politicians like to fight wars: the subject forms one of their favourite complaints. And these generals are worried.

They are far from being alone. Yesterday, a loose coalition of think-tanks, peace groups and charities including the Oxford Research Group, the Foreign Policy Centre, and Oxfam, produced a report. Time to Talk, they call it, unambiguously, "The Case for Diplomatic Solutions on Iran". Crudely put, they make three central points.

First, bombing would encourage, not deter, the Iranian regime. Flatten Natanz, if that can be done, and they would rebuild and try again. Secondly, meanwhile, you would destabilise Iraq further, if such a thing were possible, incite terrorism, threaten oil supplies, poison the atmosphere and kill a lot of civilians. Finally, the report says, the idea that diplomacy is exhausted is false. To paraphrase: some people are in too much of a hurry.

Sir Richard Dalton, formerly Britain's ambassador to Tehran, was reported as echoing that last conclusion yesterday. "Military action should be a last resort," he said, "used in self-defence against an imminent threat, and we have not reached that position yet."

In the conservative American view, all of this amounts to a pitiful, typical lack of resolve. Iran will read the signal and play the west along, with the connivance of France and Russia, until it has its nuclear weapons. In any case, Tehran, it is claimed, is much closer to achieving its ambition than had been realised. Once it is armed, the genocidal threat to Israel will become real. Once it is armed, other Middle Eastern powers, Egypt above all, will begin their own programmes. The time for diplomacy has all but gone.

One thing to notice: the people putting forward such arguments are much the same as those who promised - perhaps even believed - that Iraq would be a walk in the park. Given their credibility, just how many second chances are they allowed?

Another thing: these same people do not necessarily intend that the US itself should do the bombing. Israel believes itself ready and able. Is Israeli puissance still reliable after the botch in Lebanon? Is it the job of the US to bolster Israel's particular ambitions at every turn? Finally, is an American-backed Israeli raid likely to convince Iranians that they have been misinformed about western attitudes and strategy?

In point of fact, Ahmadinejad is growing steadily less popular at home, thanks mostly to incompetence and to his determination to isolate his country from the world. So this is the perfect moment to bomb?

Fanatics aside, many Iranians do seem to confuse national pride with a nuclear programme. They would not be the first to make the mistake. They ask the stupid question: just why shouldn't we have nuclear power or, come to that, nuclear weapons? Britain's non-debate over the Trident renewal programme makes their point. We may count as a stable democracy, trustworthy and responsible. There is nothing in international law, however, that licenses us to possess weapons of mass destruction. In any case, why not demand that certain others, say the Pakistanis, should relinquish such items?

The answer, of course, is the answer with which we began. Nevertheless, it is worth remembering that Iran's Ahmadinejad derives his excuses from the fact that non-proliferation efforts are a shambles, and a shambles born of double standards. In any case, the Islamic Republic could be entirely saintly, harbouring no ill-will whatever towards Israel or America. Nuclear weapons would still be a very bad idea. Israel's ownership of those devices is a very bad idea, indeed.

If America attacks Iran, a deplorable regime - the Iranian one, I mean - will be granted instant legitimacy. Hizbollah will strike at Israel with renewed ferocity. Fighters will flood across the border from Iran to Iraq. And Ahmadinejad, or his successor, will demand the rebuilding of each and every destroyed nuclear installation. It sounds bizarre, verging on obscene, but an Iran with its own "deterrent", invited to the big international table for the devious game of WMD poker, might just be preferable.

I wouldn't, in honesty, pretend to know for sure. I would claim that when the geniuses who brought us Iraq come up with another foolproof scheme for a spot of geo-strategic smiting, we can be certain of the virtues of scepticism. Put it this way: how do we know, after Iraq, that such people are even telling the truth about more Middle East maniacs and more filthy weapons? Would you buy a used horror story from these men?