Criticising the hit US television series South Park for being offensive is a bit like criticising Antiques Roadshow for focusing too much on old things. But this has not prevented the soul singer Isaac Hayes from quitting the show in outrage at its treatment of Scientology - ending a nine-year association with a cartoon that has left few other religious or political groups unmocked.

Mr Hayes, a Scientologist, provided the voice for Chef, South Park's resident school cook, ladies' man and love doctor. He embraced the show's ethic so fully that he reached number one in the UK in 1999 with an innuendo-laden South Park song entitled Chocolate Salty Balls.

But the singer, previously best known for the soundtrack to the 1971 movie Shaft, drew the line at an episode in which a central character, Stan, is hailed as the successor to L Ron Hubbard, who started the cult in 1952. The episode was pulled in the UK. "There is a place in this world for satire, but there is a time when satire ends, and intolerance and bigotry towards religious beliefs of others begins," Mr Hayes said in a statement. "As a civil rights activist of the past 40 years I cannot support a show that disrespects those beliefs and practices."

"This has nothing to do with intolerance and bigotry and everything to do with the fact that Isaac Hayes is a Scientologist and that we recently featured Scientology in an episode of South Park," said Matt Stone, who created the series with Trey Parker. "In 10 years and more than 150 episodes Isaac never had a problem with the show making fun of Christians, Muslims, Mormons and Jews. He got a sudden case of religious sensitivity when it was his religion featured on the show. To bring the civil rights struggle into this is just a non sequitur. Of course, we will release Isaac from his contract and we wish him well."

Since its debut in 1996 South Park has won praise, and an Emmy award, for a satirical sensibility far outstripping most American television in its sharpness. It is a mark of the respect it is accorded that guest stars gladly appear in self-deprecating roles.

The country singer Alan Jackson, whose sentimental anthem Where Were You When The World Stopped Turning commemorated 9/11, even wrote a mocking parody of his own song for a 2002 episode in which Stan and friends try to build a ladder to heaven, where the US government suspects that Saddam Hussein (subsequently depicted having a gay relationship with Satan in hell) is manufacturing weapons.