When I see this steady stream of people who once supported the invasion of Iraq, but now admit they shouldn't have, a part of me admires their honesty. But another part wants to collect them all together in a classroom while I stand in front of a blackboard snarling: "Now, why couldn't we get it right first time? We've been through this enough times before."

When I see this steady stream of people who once supported the invasion of Iraq, but now admit they shouldn't have, a part of me admires their honesty. But another part wants to collect them all together in a classroom while I stand in front of a blackboard snarling: "Now, why couldn't we get it right first time? We've been through this enough times before."

Then I'd yell: "You boy, what have we learned about the Americans when they invade somewhere?" And the columnist would mumble into his hands: "Subabmakawub". "What's that?"

"Scewavawap anmakawa."

"Come on, out with it."

"They screw everyone up and make things worse, sir."

"That's right, they screw everyone up and make things worse, now remember it for next time."

After Vietnam, Chile, Nicaragua etc, to believe that maybe this time the Pentagon would make the world more peaceful was almost charming in its naivety. But anyone who fell for it would probably not make a good scientist. They'd sit in laboratories thinking: "Hmm, so once again my experiment shows the reaction of petrol combined with fire is to explode. But let's try once more, because you never know, next time, it might cool everything down."

Whereas those people who still defend the invasion on humanitarian grounds are forced to resort to ever more surreal arguments. Now it's accepted there is widespread use of torture by the occupiers, someone will argue: "That's because under Saddam these Iraqis became addicted to torture, so we're trying to ween them off it, bit by bit. If it stopped suddenly, they'd feel dreadful withdrawal effects, but this way they'll soon be able to make do with 'torturettes', which are electrode patches you apply to your own genitals."

Or, having abandoned the idea that the invasion would bring peace, they maintain that the death and destruction is less than if Saddam was still there. This is the first time a war has been justified by the method with which governments defend economic policies. Soon they'll say: "Although the headline rate of deaths remains relatively high, the underlying trend is very much in the right direction. Indeed, if you remove certain distorting factors such as gunfire, and cases in which life has been lost, the figures are extremely encouraging."

It's amazing how one of the humanitarian benefits of invasion was supposed to be a peace deal in Palestine. So now the Israelis calmly explain they're entitled to bulldoze entire neighbourhoods because the Geneva Convention doesn't apply to them. They're like arrogant motorists who park wherever they like. If anyone gives them a ticket or a small fine for demolishing a township, they just grunt: "Bollocks to that" and rip it up.

With the war so obviously a disaster, its defenders are forced to accept the need for an exit strategy. And the exit strategy proposed is to double the number of troops, to "achieve stability, then we can exit". It's like a gambling addict saying: "I do have a strategy for giving up. I'm going to double the amount of money I gamble, then when I've won back everything I've lost so far, I'll stop."

Don't they think there was ever a similar exit strategy in Vietnam? Or do they imagine every time America increased the number of troops, it was because they were determined to break the record for the longest war in history. Perhaps Nixon read about the Hundred Years War and thought: "We could double that if we concentrate."

The blindness to history is almost puzzling. You regularly hear spokesmen saying this is nothing like Vietnam, because that war cost 60,000 lives and this one is only at around 1,000. Has it not occurred to them how the number of casualties in a war might be subject to change? Maybe they will make a statement that: "The number of dead might fluctuate slightly in a war, it may go up or down a bit, but usually it ends up pretty much the same as what you started with."

But this is what ruling cliques and empires do. They launch wars and projects to further their own interests, but claim it's for the good of humanity. Just as the British Empire produced libraries full of justifications for colonising and for slavery. And none, as far as I know, said: "It is vital to extend the slave trade because it will make us more money than you can imagine, and we're greedy bastards. Quite what God makes of it all, I can't imagine, but we'll cross that bridge when we come to it."

As the reality conflicts with the official version, the perpetrators are forced to tell ever more ridiculous stories. And that's why Geoff Hoon should be sacked - not for his role in the war, but because his lying is so feeble, full of nonsense about not knowing what was going on because he hadn't seen the newspapers that day. The next time he's caught, he'll say: "Is there a war in Iraq? My goodness, I've lost all track of the news because my wife and I have been watching re-runs of Inspector Morse on UK Gold."

And still some people fall for it. It makes you realise there ought to be a sequel to Troy, set five years after the first battle. In which a bunch of Trojan columnists say: "Ah, there's a new offer from the Greeks of another horse. We really must accept it, because I'm sure this time they really do mean it as a lovely present."