The chief rabbi, Sir Jonathan Sacks, is right. His reaction to the Anglican synod's call for sanctions against Israel is understandable. Hatred of Judaism - now commonly called anti-semitism - is a virus that has infected Christendom for two millennia. It continues to stalk the world despite its most virulent outbreak in Nazi Germany. It should not be left untreated. For too many it remains the unlearned lesson of the Holocaust. It should haunt decent Christians for generations to come.

The German pope knows that particularly well and is on the battle lines against it. On this issue, nothing divides him from the Archbishop of Canterbury and most other church leaders. If, as some now think, today's Jews are the Muslims - hatred transferred - that simply means there is a battle to maintain our common humanity on more than one front. All collective hatreds poison the body politic.

I say this as the child of a German Jewish-born father who escaped in time. His mother did not. I say it as a half-Jewish German child chased around a British playground in the second world war and taunted with "he's not just a German, he's a Jew". A double insult. But I say this too as a Christian priest who shares the historic guilt of all the churches. All Christians share a bloody inheritance.

If I feel all that in my guts and know it in my head, I cannot stand by and watch the Israeli-Palestinian conflict - one of the world's most dangerous outbreaks of collective hatred - as a dispassionate onlooker. I cannot listen calmly when an Iranian president talks of wiping out Israel. Jewish fears go deep. They are not irrational. But I cannot listen calmly either when a great many citizens of Israel think and speak of Palestinians in the way a great many Germans thought and spoke about Jews when I was one of them and had to flee.

If the Christian in me has good reason to be ashamed, so now does the Jew in me. I passionately believe that Israel has the right, and its people have the right, to live in peace and in secure borders. But I know too that modern Israel was born in terror and made possible in its present Zionist form by killing and a measure of ethnic cleansing. That is history. Tell me of a nation with an innocent history. But the Zionism at the heart of Israeli politics is about the present and the future. It makes me fear for the soul of Israel today and the survival of its children tomorrow.

The Israel characterised by the words of Golda Meir that "there was no such thing as Palestinians ... they did not exist" is an Israel that is inevitably surrounded by enemies and that can only survive militarily and economically as a client state of the world's only superpower, for now. Nor can its nuclear monopoly in the Middle East last for ever. Peace cannot be made by building a wall on Palestinian land that makes the life of the miserably conquered more miserable still. A Palestinian bantustan will be a source of unrest and violence for ever.

I say all this despairing of the Israel I love. Its people are my people. The Palestinians are my neighbours. I wish they had stronger and better leaders. I wish their despairing young people had not been driven to violence. Just as I understand Jewish fears, I understand their despair. Only an Israel that understands that too can change it. And there are Jews in Israel and in the diaspora who know it. Most of them, out of a fear of being thought disloyal, are afraid to say what they know to be true. The state of Israel has become a cruel occupying power. Occupations, when they are resisted, are never benevolent. They morally corrupt the occupier. The brave body of Israeli conscientious objectors are the true inheritors of the prophets of Israel. They are the true patriots. What nation has ever loved its prophets?

But the main objective of my writing today, is to nail the lie that to reject Zionism as it practised today is in effect to be anti-semitic, to be an inheritor of Hitler's racism. That argument, with the Holocaust in the background, is nothing other than moral blackmail. It is highly effective. It condemns many to silence who fear to be thought anti-semitic. They are often the very opposite. They are often people whose heart bleeds at Israel's betrayal of its true heritage.

I began with the recognition that the cancer of anti-semitism has not been cured. Tragically, Israel's policies feed it - and when world Jewry defends Israeli policies right or wrong, then anger turns not only against Israel, but against all Jews. I wish it were mere rhetoric to say that Israeli politics today make a holocaust the day after tomorrow credible. If the whole Muslim world hates Israel, that is no idle speculation. To count on Arab disunity and Muslim sectarian conflict and a permanent American shield is no recipe for long-term security.

There are Israelis who know all that, and there are Jews around the world who know it. In Britain, Jews for Justice for Palestinians organises to give Jewishness a human face. Tell them they are anti-semites and they will laugh bitterly, for the charge hurts deeply and is a lie. Prophets such as Uri Avnery give all this eloquent expression, but are heard by only a few. The media are afraid of a lobby that is quite prepared to do them serious damage.

Yes, of course, there are many who express their solidarity with the Palestinian people. Some are Christians. They deserve respect. If, whether wisely or not, they call for sanctions, that does not make them Jew-haters - not in theory and not in practice. My concern, however, is to express solidarity with the Israel that is not represented by its leaders or popular opinion. Once, in the days of Hitler, there was another Germany represented by those in concentration camps alongside Jews and Gypsies, the martyrs who are celebrated today. There is such an Israel too. Its voices are still free to speak, though often reviled and misunderstood. That Israel has my solidarity, as all Jews have my love and prayers.

· Paul Oestreicher was a member of the Church of England's general synod and director of the Centre for International Reconciliation, Coventry Cathedral; he is now a chaplain at the University of Sussex

paul_oestreicher@yahoo.co.uk