BETTER than three centuries have passed since anyone was strung up for blasphemy in Britain.

For some of us, that's lucky. Read through the offences for which 20-year-old Thomas Aikenhead was executed in 1697 somewhere on Edinburgh's Leith Walk and you think: "Christ, who hasn't said that?"

Or rather, that's what I think. Sometimes it's what I say. The opinions are deeply held (and all that), but personal. Where I live there are statutes, these days, to say I am entitled to hold such views. Scotland might still have a blasphemy law – no-one is entirely sure – but the risks are minimal, even on Leith Walk. Martyred Thomas died for all our sakes.

Presbyterian nutters did away with the youth pour encourager les autres. You will have met the sort. They believed they could stop other people from thinking bad thoughts if, with pomp and ceremony, they murdered a kid who had been a bit daring, as students sometimes are, possibly after having had a few.

They killed young Aikenhead because of the words that came out of his mouth. It's an aspect of faith and revealed truth that I still can't grasp. Who, being truly faithful, could possibly have their certainty, never mind their soul, put at risk by a dismal unbeliever? Which version of God – eternal, omniscient, omnipotent: the full card – could be harmed by a kid mouthing off? And which version of any God answers impertinence with executions?

Aikenhead's heinous utterances are interesting, though. Allegedly, he said the scriptures were just fables. He reckoned that Jesus did magic tricks. He observed that the Bible is full of contradictions and nonsense. With the voice of the atheist down the ages, Thomas "admired the stupidity of the world in being so long deluded". Then there was my favourite. Given the choice, Aikenhead said, he preferred Mohammed to Christ. No cartoons were supplied.

That one would still send the cat among the theological pigeons, nevertheless. Busy being "hurt", offended, or infuriated by secularists, the religious hold a single prejudice in common: each believes that all the others are dead wrong, offensively wrong, about God. Telling the Christians (reformed branch) of late 17th-century Edinburgh that their boy wasn't a patch on Islam's prophet was a neat touch.

It didn't do Thomas much good. Free speech will be scant consolation, equally, for American teenagers seeking abortions if Mitt Romney's zanier supporters come out on top.

Jokes wouldn't comfort a gay Iraqi. A Scottish journalist attempting droll remarks won't help a Pakistani child persecuted by corrupt clerics and her country's still-potent blasphemy laws. Aikenhead would be denounced by believers of all stripes even today.

The appeal to liberty of thought and expression is irrelevant to those who would kill for the sake of their loving God. People are dying because of an inept 14-minute video, Innocence of Muslims, made somewhere in California. People died because Salman Rushdie published a slightly interesting novel. People might yet die because of some cartoons in a French magazine.

To some of those professing faith, those deaths are as irrelevant as the notion of free speech.

I mean actually irrelevant. All of that Enlightenment stuff has no purchase among those who believe – those who say they know – that the only important truth in existence has been revealed. Everything else is a lie shaped for insult and harm. When they pay the price, they say, speech can never be free. All of the religious tell this story: good Catholics, honest Sikhs, truthful Jews, sincere Muslims. Opinions, they insist, can injure. Yet what do they really mean?

Some can trace a historical narrative, and the narrative hangs on a spine of facts. After the invasions, the imperialism, the economic exploitation, the racism and the massacres comes the assault on faith, the destruction of identity.

If you have witnessed Palestine, Iraq, Chechnya and Afghanistan; if you have seen your tinpot dictators acquire Western "friends"; if your mere resistance has been called a "clash of civilisations"; if you have seen the crusaders return with their drones ... To some who hold to Islam, the narrative makes sense.

It has one or two problems. These iniquities have not been inflicted on everyone who wishes to be known as a Muslim. To call 1.8 billion people homogeneous, of one mind and opinion, makes as much sense as calling me an archetypal representative of the Christian West. Christians in the West would not thank you for that.

The difference between a Saudi potentate and an Afghan peasant is vast. The difference between a Glasgow kid and a Chechen child is considerable. Egyptian intellectuals and Malay intellectuals are certainly not of one mind. Islam itself is riven – Sunni and Shi'ite isn't the half of it – in a thousand ways. Conflict with "the West" over a few French cartoons is as nothing to the bloody struggles within the faith.

Then there is the fact that some who claim to represent Islam are not averse to conflict. Anti-Semitism in the Arab world did not begin with the oppression of Palestinians. Who dubbed Innocence of Muslims into Arabic and disseminated the thing far and wide? There were theocrats keen enough to seize on the film as proof that the entire infidel West is an enemy. For them, dead diplomats and burning embassies are satisfactory outcomes.

To each statement, there is a qualification. Free speech? The Nazis liked nothing better than a joke about Jews. The magazine Charlie Hebdo might be asserting the values of the secular, revolutionary France that in 1791 abolished blasphemy laws, but the English Defence League also enjoys a cartoon caricature.

An American "pastor" liable to burn a Koran is not likely, I think, to protect my right to call him a fundamentalist gun-nut.

But let's not footle around. The argument over the right to say disobliging things over claims you happen to doubt has become bloody. Organised or not, born of Western racism or not, violent spasms in "the Muslim world" against anything deemed offensive are undermining free speech everywhere.

Self-censorship is becoming habitual for anyone who wants to avoid "provoking" a riot. Western bigots obsessed with fantasies of Islam are meanwhile rejoicing: here's their opportunity.

"You wouldn't say that to a Muslim," they will tell you should you risk a joke about the sex life, if any, of the Virgin Mary. Where's free speech, they want to know, if you don't dare to satirise Islam? They too want you to shut up. They overlook the obvious: I don't believe any of it.

The Prophet ascended through the seven heavens? Why do they all ascend? There was a virgin birth? Would Romney's evangelicals fall for that one on the picket line at the abortion clinic? And where do we all stand, my chums in God, on the question of those gay people? I see: East or West, you are united in vicious contempt.

Friday was declared "a day of love for the Prophet" by the government of Pakistan. Muslims around the world no doubt embraced it as such. Many others, treating faith as war by other means, were less clear about the concept. They have their counterparts in the West among fraudulent champions of liberty.

The point of free speech is to say so. Words alone never killed anyone, but people who fear words are murderous. That can't be said too often.