For months - years even - the historical twinning that some campaigners have chosen for the situation in Gaza has been with the Warsaw ghetto. There'll probably be a sign up soon, because in the past week Ken Livingstone, the activist-musician Brian Eno and George Galloway have all made the comparison.

“Gaza is a ghetto,” said Mr Livingstone, "in exactly the same way that the Warsaw Ghetto was, and people are trapped in it”; while Eno predicted: “They [the Israelis] will continue to create a Warsaw Ghetto in the Middle East.” The less-restrained Mr Galloway pronounced: “Those murdering them [the occupants of Gaza] are the equivalent of those who murdered the Jews in Warsaw in 1942.”

Busy people sometimes hurry their reading. Mr Galloway, for example, may only have skimmed the day-by-day reports made by SS Brigadeführer Jürgen Stroop on the destruction of the Warsaw Ghetto in 1943. On the third day of the operation Stroop tells how “large numbers of Jews - entire families - already on fire, jumped from the windows. We made sure that these, as well as the other Jews, were liquidated immediately.”

Stroop's operation was made necessary because the inhabitants of the ghetto took up what few arms they had, having already seen more than half their number transported to extermination camps - a figure which, if translated into Gaza terms, would mean the deliberate killing of 500,000 Palestinians.

A year earlier in this place that was, pace Livingstone, “exactly” a ghetto in the same way as Gaza, the death rate from starvation and disease was more than 4,000 a month - the equivalent of 12,000 in the Gazan “ghetto”. On these grounds alone, never mind any others (rockets, Hamas, etc), we may conclude that Gaza 2009 and Warsaw 1943 have very little in common.

So why the philistine insistence on this particular match? Partly, I imagine, so that the matcher can mention the “irony” of Jews supposedly doing to others what the Nazis “did to them” - as if there weren't a thousand other closer, but far less narratively satisfying, comparisons.

But this ahistorical hyperbole is also the product of a kind of binary thinking, the belief that there can only be two kinds of anything, and two possible responses: there's the good and the bad; there's the victim and the murderer. The only way Jews can shed their unique victim status is if they take on the mantle of the worst kind of murderer, the mantle of Stroop. The only way we can think about the Holocaust (or subsequent little holocausts) is that those who carried it out are so unlike us that they are beyond comprehension.

Strangely this thought did not begin for me with events in Gaza, but in the reactions to a piece of cinema released here last week. Ten years ago I read a book by a German author, Bernhard Schlink, called The Reader, which told the story of a young German boy who, in 1958, falls for an older woman. She becomes his first lover, but then disappears from his life. A few years later, as a law student he sees the same woman - Hanna - on trial for crimes committed as a guard at a concentration camp during the war. Gradually he realises that the key to much of her behaviour, exciting and appalling, lies in something as banal as her shame at her own illiteracy.

The film version, starring Kate Winslet, directed by Stephen Daldry and with a screenplay by David Hare, has met with a surprisingly vigorous dusting-up from some of the Anglophone world's finest film critics. The objections to style or cinematography vary, but those to moral purpose are very similar. “Outrageously,” said the New York Times reviewer, “Hanna is a victim too, because she took the guard job only to hide her illiteracy, as if illiteracy were an excuse for barbarism.”

Anthony Lane, of The New Yorker, more languidly complained that the audience is “encouraged to muse upon the cultural shortcomings, or improvements, in the life of an ageing member of the SS. This is not an issue that most of us feel the need to worry about.”

As an assertion, it seems to me, this is more or less completely wrong. But I'll come to that in a minute, after having said that I think neither the book nor the film deserve such castigation. On the contrary. Neither invite you to think that Hanna is a good person or a victim, indeed she is rather animalistic, manipulative and lacking in imagination. And neither excuses barbarism in any way. But the story suggests that, if you didn't know your lover was once a concentration camp guard, you wouldn't necessarily be able to tell.

Wilfully, almost, the critics have missed the point. One of the most important exchanges takes place in the courtroom. Hanna, who joined the SS as a guard in 1943, is being interrogated by the judge about how selections were made in her work camp for those who would be sent to the gas chambers. She answers matter-of-factly that each of the six guards selected ten women every month. The judge is horrified. “So what would you have done?” she asks, genuinely bemused.

In an interview Daldry talked about how the real trials were reported in the German press in the 1960s. Those in the dock had been depicted as “obviously monsters, sadists, mad people, criminally insane. They must be because only the criminally insane could have been involved in this.” He was talking about the binary, evading thought. Schlink, Daldry and Hare are about challenging this evasion.

So when Hanna asks “What would you have done?” the answer is, how far back shall we go? When 13.75 million German voters put their cross against the overtly Jew-hating National Socialist list in July 1932, didn't they make themselves complicit in the events that ended up with Hanna's choice? Or, to put it another way, couldn't people that you might fall in love with, be capable - depending on the circumstances, created by millions of others - of doing terrible things? That's the question the New Yorker critic so disdains.

It has always seemed to me that the most awful question raised by the Holocaust is not about victimhood, but about being the perpetrator, and how that declension can take place. And in that context I want to ask Brian Eno, whether he has ever - in a recording break - watched Hamas TV and thought to compare it to the propaganda, much earlier, of those who later gave the Hannas their jobs?

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