In his memoirs, published last year, Ken Livingstone referred to "several commentators and minor intellectuals" who, he said, had become obsessed with Islam. These included Christopher Hitchens, Nick Cohen, Martin Bright and me.

Cohen, at least, was unfazed by the accusation, but I was angered. I've written little about Islam. That output, moreover, is devoted to defending Muslims against campaigns such as the Swiss vote to ban the construction of minarets and rebutting claims that Europe faces a demographic threat from Muslim immigration and birth rates.

I recalled his insinuations last week when reading complaints by Mehdi Hasan, the political commentator. Writing in the Guardian, Hasan recounted the malicious online abuse he consistently receives. A wider problem is "relentlessly hostile coverage of Islam", for which he holds some in our profession culpable.

British commentators, Hasan says, can be divided into three groups: those who regularly condemn anti-Muslim bigotry (who include Jonathan Freedland, my fellow JC columnist); those who promote it with stereotypes; and the third and largest group, "those commentators who boast otherwise impeccable anti-racist credentials yet tend to be silent on the subject of Islamophobia".

I suspect, though don't know, that Hasan counts me in that third group. In any event, I count his typology no less tendentious, if a lot more thoughtful, than Livingstone's.

I challenge treating belief and ethnicity as equivalent

There is something disturbing in public discourse about Islam. A segment of opinion cannot distinguish between Muslims and the theocratic fanatics of al-Qaeda. It holds to a conspiracy theory that genuinely does recall the ancient prejudice, given modern garb in the Protocols of the Elders of Zion, against the Jews. This is not only a problem but a pathology and an evil.

Note, however, where Hasan's argument then goes. It indicts anti-racist commentators who are insensitive to "Islamophobia". And here, while accepting that conspiracy theorists make little of such distinctions, I protest against treating belief and ethnicity as equivalent. Once you accept that elision, mayhem awaits.

A democracy will uphold freedom of conscience, belief, assembly and worship. Following Thomas Jefferson, it will eradicate religious discrimination in public office. But the defence of a system of religious belief and affiliation is not the same thing.

If you commit yourself to combating hostile portrayals of Islam, what principled reason would you have to oppose banning books and cartoons that deride people's deeply held beliefs? At best, you might treat free speech as a right to be balanced against other social goods, such as tolerance and social cohesion. And that's a lethal assumption. A free society depends on criticism, including derision and mockery, so that bad ideas rather than their adherents perish.

When I speak to Jewish audiences, I typically explain my support for Israel. As an atheist, I have no interest in the fortunes of Judaism; but I have a powerful interest in the flourishing of the Jews, for which a secure Israel in a two-state solution is essential. On similar grounds, I supported Western intervention to defend the Muslims of Bosnia and Kosovo from genocidal repression by Milosevic.

So when Hasan challenges pundits whether we are with him in standing against "the Islamophobes", I say this. I defend free speech and deprecate the abuse he suffers. I condemn populist campaigns depicting Muslims as a homogeneous, threatening force. I support religious liberty, pluralism, and the rights of persecuted peoples. But adopting the neologism of "Islamophobia", analogous to xenophobia, is another and extraneous matter. I'm not buying it.

Oliver Kamm is a leader writer for 'The Times'