First, I should declare an interest. I am a friend and admirer of Rabbi Jonathan Wittenberg, leader of Britain's Masorti movement. But I also like and admire the JC's political editor, Martin Bright. So where to stand after Rabbi Wittenberg was branded by Bright a "useful idiot" for participating in an event also addressed by an official of the East London Mosque, an institution that has hosted speakers with vile views?

Bright's evidence cannot be brushed aside easily. The uncomplicated response would be to boycott the ELM and anyone connected even tenuously to it, denying them whatever legitimacy they gain from a Jewish presence.

But it's not so simple. For one, Wittenberg is not the only rabbi to have had dealings with the ELM. Just weeks ago, four rabbis - including the Orthodox Dayan Binstock - spoke at the mosque's community centre. Yet the JC has not denounced Binstock as a "useful idiot", nor has it railed against the Orthodox Fieldgate Street Great Synagogue, whose president tells me they have a "wonderful relationship" with the nextdoor ELM. In fact, I've separately learned the shul was delighted to accept a £5,000 contribution from the mosque towards a new roof - made with no publicity - and was touched when the mosque halted building work to ensure they could daven undisturbed on Yom Kippur. Are the Fieldgate Street congregants "useful idiots" too?

Odder still, it's not as if Wittenberg and his New North London shul have a formal tie with the ELM. What roused Bright's ire was that Wittenberg spoke at an event also addressed by an ELM representative. The event was organised by London Citizens, a coalition of some 200 organisations, including trade unions and faith groups that campaigns for, among other things, a living wage. Bright branded the rabbi a "useful idiot" not because Wittenberg had embraced some fire-breathing extremist, but because he works with a group, London Citizens, one of whose many affiliate organisations has invited speakers with noxious views.

In similar vein, last year the JC denounced the Pears Foundation for giving money to a group which had, unbeknownst to Pears, once invited to a reception a man who, unbeknownst to the group, had once known the 7/7 bombers. The target - Pears or Wittenberg - is attacked not for consorting with the devil, but for consorting with those linked to those who are linked to the devil.

The safest response would be to meet no-one outside

Of course, Jewish leaders must be vigilant. Some hardcore Islamist reactionaries do seek validation by association with credible figures. The safest response would be to circle the wagons and meet no-one outside. That way we could be sure there were no unsavoury characters lurking in the shadows. We would talk only to ourselves.

Nonsense, comes the reply: there are plenty of Muslim moderates we could meet. Trouble is, most are rapidly deemed beyond the pale by our community's self-appointed gatekeepers. Mohammad Aziz of the ELM, for one, has impressed Jewish groups with his openness and - confirming that the ELM is no monolith – attended Limmud. But he has been monstered by the anti-Islamist Harry's Place blog as a dangerous radical. Are there more than a handful of Muslim leaders the watchdogs would deem acceptable? And would that handful be as unrepresentative of British Muslims as, say, Jewish radical anti-Zionists are of British Jews?

It's easy to have dialogue with those you agree with. Far harder to talk to those who disagree, forcing them to rethink the stereotypes they have of your community. That's what Rabbi Wittenberg does. It would be more comfortable for him to stay inside our cosy Jewish bubble but he dares venture outside. He should not be condemned for that. He should be praised.