You are likely familiar with the story, of how students at the London School of Economics advertised their Atheist, Secularist and Humanist Society by wearing T-shirts that are utterly innocuous in their content, save that they depict the prophet Mohammad. The LSE demanded that the T-shirts be covered up but subsequently apologised for their heavy-handed action.

The issue featured on the BBC's The Big Questions leading to the Liberal Democrat parliamentary candidate Maajid Nawaz, a Muslim, tweeting the cartoon and stating that he was not offended by it. Less tolerant Muslims are now calling for his deselection and even threatening his life. In the resulting publicity Channel 4 News showed the cartoon but censored it owing to the "offence" it might cause, while the BBC's Newsnight refused to show it at all.

What heinous outrage lurks beneath Channel 4's black oval?

First, we need to continually remind everyone that freedom of speech does not stop at speech that offends someone. Anyone saying that they believe in free speech "except when it crosses the line to being offensive" does not believe in free speech. Indeed, it is only speech that someone objects to that needs protection.

Second, TV programmes and newspapers routinely include material that is offensive to some. Broadcasters receive a regular stream of complaints from people offended by bad language, sexual content or explicit violence. Yet the broadcasters don't try to please everyone, they instead include warnings about such content so that the viewer may choose not to view.

Third, satirical cartoons and critical comment are routine in the Western world; every major politician is regularly lampooned in ways that people could, if they chose, find offensive.

Fourth, religious taboos are rules that one may impose on oneself, but not on others. That basic principle is the very core of religious freedom in a secular society. Some might choose not to eat pork or cheeseburgers and others might choose not to write the word "God" or switch a light switch on the Sabbath. It would, though, be utterly wrong for anyone to impose such religious taboos on a wider society.

Yet that is essentially what is happening. Some factions of Muslims (but not all) are demanding that everyone observe their taboos, and the British newspapers and broadcasters are acquiescing, either from a misguided desire to avoid offence or out of fear of repercussions. By acquiescing they send the tacit message that the demand is a reasonable one. That encourages others to accede to the same demand, and gives the impression that those who don't are being uncouth and irresponsible. It also emboldens those asking for the censorship, encouraging them to make more demands. Lastly, siding with the Muslims who want censorship undercuts those Muslims who accept the free speech of a liberal society, people who should be the natural allies of a free press.

The broadcasters have been uttering weaselly words about avoiding offence and about the nature of the cartoon being "not integral to the story". If this were about any other religion or any other issue they would not take that line. In every other news item about controversial images they show the image and allow the viewer to form their own opinion. As just one example the footballer Nicolas Anelka is in trouble for a "quenelle" gesture that is offensive to Jews, and yet the video of his gesture has been widely broadcast on news bulletins.

Why is this different? It's different because Channel 4 and the BBC feel that they are obliged to observe an Islamic religious taboo, one demanded by some parts of a minority religion. It would be as if the BBC refused to write the word God simply because a few Jews avoid doing so. This is against every principle of secular freedom. It would be understandable for a specifically Islamic media outlet to adopt Islamic mores, but Channel 4 and the BBC are nationally funded organisations, there for all of us.

The adoption of this censorship is as wrong as if they allowed a minority fringe group to dictate permissible sexual content or bad language in television drama, or if they allowed a fundamentalist Christian sect to dictate the permissible portrayal of gay characters, or if they allowed an extreme racist group to censor the use of black actors.

We are surely well passed blasphemy laws, and should not accept new ones demanded by fringe minorities, however vocal. Satirical cartoons lampooning important persons are normal in our society and thus self-imposed censorship is a betrayal of our long tradition of a free press.

Channel 4's excuses include the suggestion that leaving Jesus visible in the censored cartoon would not offend because Jesus "is commonly depicted in cartoon form". There is the solution. This attempt to impose an Islamic taboo on the whole of society has to be met by those who believe in secular free speech taking every opportunity to flout it.

@coelhellier blogs at coelsblog.wordpress.com