An NHS conference on conflict resolution for managers and union representatives has turned into a sobering lesson in how conflicts are decidedly not resolved. The guest lecturer at the conference, organised by the Manchester Mental Health and Social Care Trust, was to be Moty Cristal, an expert in negotiation theory and mediation. But under pressure from one of the participating unions, Unison, his invitation was unceremoniously withdrawn. The reason? He is an Israeli.

At no stage, it should be emphasised, was any concern raised about Professor Cristal himself. He is, by all accounts, an expert in his field. He has lectured around the world and in the UK, including to the Muslim Council of Britain, and has been an active participant in Israeli-Palestinian negotiations and back-channel dialogue. It was his Israeli nationality alone, he was informed, which made his participation "unacceptable given Unison and TUC policy on the Middle East conflict".

This is not the first time a supposedly political boycott has seamlessly morphed into bigotry and prejudice. When two Israeli academics were "unappointed" from the editorial boards of journals at Manchester University, – again purely on the grounds of their citizenship – one of them, Gideon Toury, observed wryly: "I was appointed as a scholar and unappointed as an Israeli."

The surfacing of pure discrimination in the guise of a political cause is only one warning siren about boycott campaigns claiming to advance a progressive agenda. Another is the revealing selectivity with which they are applied. But the most frustrating is the troubling way in which such campaigns inevitably set out to silence the very voices that anyone truly seeking peace would want to support.

A current example is the campaign to press the Globe Theatre to withdraw an invitation to the Habima theatre company, the oldest Hebrew language theatre group in the world, from performing as part of the World Shakespeare Festival accompanying the London 2012 Olympics. Of the 37 participating theatre companies, Habima is the only one subject to such a call. Yet Habima, with its cast of Arab and Jewish actors, and a repertory which repeatedly challenges Israeli establishment dogmas, is precisely the kind of voice that progressives should be supporting, rather than undermining.

So, too, is the Histadrut, Israel's trade union, which represents many thousands of Israeli Arab members. It has close relations with its Palestinian counterpart, the PGFTU, working with it to advance the rights of Palestinian workers, and on other joint initiatives to advance coexistence and workers' rights. Yet a concerted campaign is urging the TUC to break all ties with the Histadrut, while Unison already practises such a boycott.

By their nature, boycotts target places of connection and interaction, the very arenas in which dialogue and dissent are most likely to occur. Their insistent focus on censoring academics, cultural events and professional ties target in practice the very elements of society which anyone interested in fostering understanding should be wanting to bolster.

There is, to be sure, an appealing simplicity about a boycott strategy. It requires very little effort, demands no grappling with annoying complexities, or the making of challenging distinctions between moderates and extremists. Most appealing of all, it absolves one of any need to examine possible shortcomings on one's own side.

Yet anyone concerned about building Palestinian society, rather than simply trying to demolish Israel, realises the futility of this approach. Though a staunch opponent of Israel, Edward Said cared enough about advancing Palestinian interests to recognise this: "What have years of refusing to deal with Israel done for us?" he asked. "Nothing at all, except to weaken us and weaken our perception of our opponent."

It is sad – and revealing – that supposed pro-Palestinian activists campaigning to prevent the Habima theatre from performing are doing nothing to support Ashtar Theatre of Ramallah, which is having difficulty selling tickets in the same festival. Those who care about building the foundations for reconciliation and peace will recognise that these are the voices they should be working to amplify, not to silence.