John Berger and the Israel Boycott

Of the intellectuals and artists who have signed on to the cultural boycott of Israel, the one I respect most is John Berger. His name is also used extensively by PACBI because he's recognised across the world, unlike all but one or two of the other signatories. Arundhati 'all multinationals are evil except those that publish my books' Roy is the other big name, but then, has anybody come across a boycott that Arundhati Roy doesn't support?
I wanted to know more about John Berger's position on the issue, and found the letter he wrote in favour of ostracising the Zionist Entity. Here it is:

"Boycott is not a principle. When it becomes one, it itself risks to become exclusive and racist. No boycott, in our sense of the term, should be directed against an individual, a people, or a nation as such. A boycott is directed against a policy and the institutions which support that policy either actively or tacitly. Its aim is not to reject, but to bring about change.
How to apply a cultural boycott? A boycott of goods is a simpler proposition, but in this case it would probably be less effective, and speed is of the essence, because the situation is deteriorating every month (which is precisely why some of the most powerful world political leaders, hoping for the worst, keep silent.).
How to apply a boycott? For academics it’s perhaps a little clearer - a question of declining invitations from state institutions and explaining why. For invited actors, musicians, jugglers or poets it can be more complicated. I’m convinced, in any case, that its application should not be systematised; it has to come from a personal choice based on a personal assessment.
For instance. An important mainstream Israeli publisher today is asking to publish three of my books. I intend to apply the boycott with an explanation. There exist, however, a few small, marginal Israeli publishers who expressly work to encourage exchanges and bridges between Arabs and Israelis, and if one of them should ask to publish something of mine, I would unhesitatingly agree and furthermore waive aside any question of author’s royalties. I don’t ask other writers supporting the boycott to come necessarily to exactly the same conclusion. I simply offer an example."

This is a nuanced position and one that I have no problem with. It was obviously motivated by a particular event, which gave it urgency: Israel's indiscriminate bombing of southern Lebanon in 2006. That's why Berger wrote, "Speed it of the essence, because the situation is deteriorating every month".
Unfortunately, John Berger hasn't always kept to his principle that the boycott's "application should not be systematised; it has to come from a personal choice based on a personal assessment." Earlier this year, after Ian McEwan explained why he would accept the Jerusalem Prize, Berger signed a letter urging him to reconsider, and calling the Prize a "corrupt and cynical honour", "a cruel joke and a propaganda tool for the Israeli state".