RICHARD Wagner, whose bicentenary is being celebrated this year, was a small man (about 5ft 4in) with a very big head who was noted for his vicious temper and his diseased anti-Semitism.

He was also a composer of genius.

Born in Leipzig, the son of a policeman, he had an early reputation as a brawler and street fighter. He developed into a prolific writer and journalist – and one of the most celebrated creative artists Germany has ever produced.

He has plenty of apologists. Some of them claim that his anti-Semitism was rooted in his unhappy years in Paris, where he desperately tried, and failed, to get his opera Rienzi performed. He believed that those who rebuffed him were Jews, and he also hated being in hock to Jewish moneylenders.

He was undoubtedly very poor and desperate at this stage in his life, but that is no excuse.

His anti-Semitism was thorough and deep, not a passing phase; he expounded it in his infamous treatise Judaism in Music. It is not by chance that he was Adolf Hitler's favourite composer. Some have even suggested that his writing, if not his music, helped the rise of Nazism.

To mark the 200th anniversary of his birth, the Royal Opera House in London will soon be staging a controversial show by Simon Callow which will expose the composer's rampant prejudices. Indeed Callow says that the composer's anti-Semitism was so repulsive that he found it almost "toxic" to deal with.

At the same time Wagner remains much loved, and much performed, the world over. Recently the London Proms opened with a triumphant production of his Ring cycle, conducted by Daniel Barenboim, who is himself Jewish.

Many opera lovers sincerely believe that you can enjoy the art while ignoring the artist's opinions. And indeed many great creative artists have held vile opinions, and behaved very badly – possibly painters in particular. You can surely separate the art from its creator.

There is the related question of whether great art can have powerful political significance, for good or ill – and I certainly find it hard to see how it can exist in some pure and rarefied artistic world, divorced from the everyday social and political world that we all have to live in.

At the same time the very greatest art can be so subtle and complex that you cannot really find any direct "message" or propaganda in it.

Shakespeare's Merchant of Venice is a case in point. One of his finest plays, it is directly about Jewishness, and anti-Semitism. It is quite possible that anti-Semites will contrive to find in it plenty to support their noxious views.

And yet Shylock's eloquent speech: "If you prick us, do we not bleed? If you tickle, us do we not laugh? If you poison, us do we not die? If you wrong us do we not, shall we not, revenge?" is a plea on behalf of more than just himself. So Shylock is not just one man, he becomes the spokesman for Jews the world over, and in all time.

Shylock is clearly determined to take revenge for all the prejudice he has endured. He becomes almost deranged with hatred, and when Portia makes her noble and moving speech about mercy, Shylock dismisses it. He wants revenge, not mercy.

Audiences have been known to boo and hiss Shylock, so powerful is the play. But surely they are not booing and hissing him because he is a Jew, but because he is a Jew contorted by hatred.

I have never heard of any production of the Merchant of Venice being banned, but Wagner's operas are less lucky. Just last year a major performance of his work in Tel Aviv was called off after forceful protests.

That is censorship, of a kind, and most civilised people are pretty wary of censorship. If the state, or indeed the mob, act to prevent supposedly offensive art being performed, we are entering dangerous territory.

Wagner was a repellent human being, but his art should not be banned.