"If you like the president's politics, you probably like his voice and appearance as well". So writes social psychologist Daniel Kahneman in his wonderful book Thinking Fast and Slow. The Nobel laureate used the example to introduce his readers to the "Halo Effect". And I was thinking of it last weekend when reading Archbishop Desmond Tutu's extraordinary Observer article explaining why he would not share a platform with Tony Blair.
The Halo Effect explains why chief executives, disproportionately, are tall people. And why people admire the truly dreadful poetry of Harold Pinter.
It's because everyone likes their thoughts to be ordered and coherent. It is hard to cope with the thought that someone who is hugely admirable in one way is not so in another. That's why people are anxious to believe that their favourite pop star is also a nice person who tips waiting staff generously.
And it's why it is hard to cope with the idea that the archbishop, an anti-apartheid hero, is capable of such sloppy thinking. And that he may be morally, and not just technically, wrong.
The technically wrong bit I think we can deal with pretty quickly. The archbishop wants Blair tried in the International Criminal Court (and is impatient that he has not been) for offences which, as professor Norman Geras has repeatedly pointed out, are not yet indictable before the ICC.
Not a minor error but one that, I guess, one could leave to one side, if swept along by the rest of his argument. If only one were.
Desmond Tutu is against the war as he always has been. I do not agree with him, as I always haven't. He thinks Blair lied. I don't. Perhaps you think he was right, perhaps you think he wasn't. I don't want to go over all that again, because it won't get us anywhere.
Had he merely rehearsed the old points, I wouldn't have bothered with this column. But, in his second paragraph, he made a point so bizarre, I couldn't just leave it alone.
Here it is: "The then leaders of the US and UK fabricated the grounds to behave like playground bullies and drive us further apart. They have driven us to the edge of a precipice where we now stand - with the spectre of Syria and Iran before us."
What on earth does this mean? Does it mean that if we had not invaded Iraq, Syria would not be facing a rebellion? It can't mean that, because if it were true that would surely be an argument for the Iraq invasion (that it sparked democratic resistance elsewhere in the Middle East) not against it. And, in any case, that explanation leaves the mention of Iran hanging there.
So perhaps it means, that because of the Iraqi invasion we now face the spectre of an invasion of Iran and Syria.
But, again, no, it can't mean that because it is so obviously the case that the invasion of Iraq has reduced the chance of military action elsewhere.
My conclusion is that the archbishop means something much more hazy and incoherent but nevertheless interesting. He is arguing that war is sort of catching and that, if only the Americans and British had been nicer to Saddam, then other bad things wouldn't have happened. Like, erm, Syria and Iran. I think.
And the problem with such thinking is not that it is hazy, it is that it is wrong. Because it is saying that, if you never act, never do anything to combat aggression, the result is peace. And, if you act, you are to blame for bad, violent, things that happen everywhere. Which makes it, in one-and-a-half perfect little incoherent sentences, the keystone argument against everything Israel does to protect itself.