The despicable attacks on human-rights organisations investigating Israel's Gaza offensive in January confirm Churchill's observation: "A lie gets halfway around the world before the truth has a chance to get its pants on". The mission led by the South African judge Richard Goldstone to investigate international human rights and international humanitarian law violations during Israel's offensive, established by the UN Human Rights Council (UNHRC), is the latest victim. The knives have been out for the mission for months. Now they are being plunged into him and his colleagues.

The New York-based Human Rights Watch (HRW) has assiduously responded to a deluge of scurrilous attacks on its credibility and staff, yet totally unfounded allegations — for example, about accepting Saudi government funding and failing to give a critical report to the Israel Defence Forces before releasing it to the public — are constantly being recycled. HRW messed up by failing to see that the nerdy and, to most people, disturbing hobby of its weapons expert Marc Garlasco (he collects German and American Second World War memorabilia) could be used to discredit his role as author of highly critical reports of Israel's military conduct in Gaza. But when this story broke last week, the equation implied in some allegations — ‘Nazi' object-collector plus ‘Israel-basher' equals ‘anti-Semite' — was baseless and defamatory. That he also worked on reports critical of Hamas and Hezbollah was ignored. As another excuse to attack HRW, and deflect attention from its reports' findings, the Garlasco affair was a gift.

The human-rights world is not beyond reproach. UNHRC has hardly been impartial on Israel. Goldstone accepted his role only after the council president agreed to the alteration of the mission's mandate to cover all parties to the conflict, not just Israel. But mistrust alone does not explain the extraordinary scale of the attacks on human-rights organisations, including all Israeli ones, for their reports on Israel.

In the 1970s, Jewish groups pressing the Soviets to allow Jews the right to leave the USSR worked with the human-rights movement and based their arguments on human-rights principles. But now the promoters of the concept of the ‘new anti-Semitism' — that Israel is the collective Jew persecuted by the international community — hold the international human-rights movement largely responsible for it. Unable to face the fact that occupation and increasingly extreme rightwing governments turned Israel into the neighbourhood bully, and misreading the fallout for Jewish communities as abandonment by progressive forces and governments, many Jewish leaders and opinion-formers have become the human-rights movement's fiercest critics. With anti-Semitism framing this attack, reasoned argument becomes nigh on impossible.

Does it then come down to a matter of whose reputation you trust? If so would it be critics of human-rights agencies like Alan Dershowitz, the prominent American lawyer who thinks torture could be legalised, Melanie Phillips, a columnist who calls Jewish critics of Israel ‘Jews for genocide', and Gerald Steinberg, who runs NGO Watch and is an advisor to the Lieberman-led Israeli Foreign Ministry? Or Richard Goldstone, former chief prosecutor of the International Criminal Tribunals for the former Yugoslavia and Rwanda, who is putting his considerable reputation on the line in taking the UNHRC assignment? Frankly, I don't think there is a contest.

By declaring the reports of human-rights agencies biased, the attack dogs are reinforcing the damage Israel is doing to itself. They put Israel in the company of serial human-rights abusers that make the same complaint. And by refusing to respond to letters from HRW, denying the Goldstone mission entry to Israel, rubbishing testimony from Gazans unless it supports Israel's version of the offensive, and allowing the army to investigate itself, Israel merely shows it cannot even tolerate reasonable criticism. This is a sign of weakness, not strength.

Goldstone, meanwhile, has attracted extra venom from some who label him a traitorous Jew. Would they say the same about another Jew, Ren Cassin, one of the prime drafters of the 1948 Universal Declaration of Human Rights? Cassin was deeply influenced by the Holocaust, and the universal declaration was drawn up in direct response to it. It contains the bedrock principles upon which today's human-rights agencies base their work. Judge Goldstone is heir to Cassin's legacy.

For NGO Watch, Netanyahu and others attempting to discredit human-rights agencies, Palestinian and Israeli human rights are in conflict. For Cassin, human rights were about morality; respect for the inherent dignity of all men and women. His vision, promoted by human-rights bodies, offers hope for human progress. We owe it to Palestinian and Israeli alike to listen to Judge Goldstone with open minds — he might just bring us closer to the truth of what happened to human dignity in Gaza in January 2009.