On Tuesday evening, a furious crowd gathered outside the London's Barbican Centre, chanting, waving placards, banging drums, and blowing whistles. What had provoked their rage was an exhibition at this leading arts centre - but no ordinary exhibition.

'Exhibit B' featured a series of rooms in which black actors portrayed both historical human exhibits in cages and chains as well as modern-day asylum-seekers. It was based on the grotesque 'human zoos' of the 19th and early 20th centuries, in which Africans were displayed like zoo animals for the paying public, under the guise of 'ethnological enlightenment'.

This is the latest work of white South African director Brett BaileyBailey comes from an affluent South African background and in his early life the only black South Africans he knew were servants. But after the end of apartheid in 1994 he began to take a deep interest in the racism that had divided the country.. It has already been performed in 12 cities across the world and has been viewed by more than 25,000 people.

The Barbican says it is intended to confront 'the abhorrent historical attitudes to race during the colonial era' and so far it has attracted many glowing reviews. One critic called it 'both unbearable and essential'.

Yet others say it is racist and offensive, and as a result of the protests, many organised by black groups in the capital - and a 20,000-strong online petition - the exhibition has now been cancelled. Some find it particularly insulting that a subject of such importance to black people has been directed and curated by mostly white people - although most of its black performers have defended it.

One critic has likened it to a show with Jews in gas ovens or a London gallery displaying jihadist art work celebrating then 77 bombingsA series of suicide attacks in London in 2005 on underground trains and buses which killed 52 people and injured many hundreds more..

Some serious critics believe that censorship may seem hard to defend, yet it can be a vitally important method of minimising social friction and protecting people's dignity. Some topics are just too sensitive. If a work of art is so controversial as to inspire protest and violence, as Salman Rushdie's 'The Satanic VersesIn 1989, the Iranian leader, Ayatollah Khomeini, called for the author's execution after he wrote the novel inspired by the life of the Prophet Muhammad. Several attempts were made on Rushdie's life as well as on the lives of his translators. His Japanese translator was stabbed to death in 1991.' did, then it should be censored. Just because censorship can be controversial, doesn't automatically mean we should never ban anything.

But a more common view is that one of art's functions is to provoke a reaction and make us think. That is the whole point of 'Exhibit B'. It is alarming that one single noisy protest has bullied such a prestigious art centre into closing its doors. What is more, nearly all of those who condemn the exhibition as offensive have not seen it. Many of those who have - and its black performers - say it is respectful and powerful. To say that it is impossible for us as humans to be able to empathise with the plight of others, of whatever race, is pernicious and troubling.