In ancient Persia, which is now Iran, there lived at the beginning of the third century a prophet by the name of Mani.
He developed an exhaustive cosmology which saw the world as caught up in a struggle between a good spiritual realm of light, and an evil material force of darkness.
It's a world view whose influence has never quite been vanquished, as our former prime minister Tony Blair demonstrates.
His Manichean instincts were to the fore again last week when he said in the BBC interview to plug his new book: "I think it is wholly unacceptable for Iran to have nuclear weapons capability. I think we've got to be prepared to confront them, if necessary, militarily."
I had never expected Blair to apologise for the war in Iraq. Even if he wanted to, he could not; those who were against it would not be appeased and those whose soldier sons had died for their country might well feel betrayed if he were publicly to concede that their sacrifice had been demanded in error. But I had thought that, in his heart, he might know that it had all been a ghastly misjudgement. Not so, for the messianic glint was once again in his eye.
No one should have any illusions that Iran today is a very nasty place. Carla Bruni, the wife of President Sarkozy of France, discovered that last week when a state-run newspaper in Tehran labelled her a prostitute who should be stoned to death. Her offence had been to criticise the Iranian regime for sentencing a woman to death for adultery.
The sentence on the woman concerned, Sakineh Ashtiani, is under review after an international outcry. (She may now be hanged rather than stoned). But two other people received the same sentence for alleged adultery in Iran last week, so international opinion clearly has not had that much influence.
But it is not only a barbaric judicial system that makes Tehran so unpleasant. Its democracy is a sham, as the rigged presidential elections last year showed, along with the violence against the supporters of the defeated candidate. Thousands of protesters were detained; 80 have been jailed and 10 sentenced to death.
Just last week, pro-government militia attacked the home of an opposition leader while the police looked on.
But should the response be to bomb Tehran? There is a weary familiarity about the scenario. We saw it in Afghanistan and then Iraq and Iran seems next. First the place is denounced as a strategic threat. Next a casus belli is found: Afghanistan was hiding Osama bin Laden; Saddam supposedly had weapons of mass destruction; Iran is suspected of developing a nuclear bomb. Then come sanctions; we are currently in the fourth round against Tehran. And finally, inexorably, comes the "last resort": military action.
Iran has a developing programme to acquire nuclear power. To the north, Russia has the bomb. To the east, Pakistan and India have too. To the west, Israel has an estimated 400 nuclear warheads.
To fuel its nuclear power stations Iran is enriching uranium. But enriched uranium can also be used to make the fissile core of an atom bomb.
But is it worth going to war over?
The elaborate game of bluff and double-bluff suggests not.
There is a lot of bluster about. But all the war-gaming exercises done by the Pentagon show that an air assault on Iran's carefully dispersed and buried nuclear sites would produce outcomes worse than living with an Iran with a nuclear weapon capability. The bombing would be a propaganda gift to anti-Western extremists. Terrorists from all over the world would report to Tehran for duty.