You know Christmas is coming when the papers begin to fill up with stories of well-meaning and cloth-headed persons trying to avoid the terrible threat represented by mentioning the Christian origins of Christmas (the clue is in the name...). It is so obviously offensive to be reminded that singing about peace and goodwill started two millennia ago, for a very particular reason, on a hillside in Bethlehem.

The delicate and sensitive public — impervious to industrial levels of cinematic violence and internet trolling — has to be protected from this appalling truth.

But this year the screw has been turned further with the decision of certain cinemas to ban an advertisement featuring an assortment of fairly average British citizens saying the Lord’s Prayer. Now, when I go to the cinema (not very often, I admit), I have to sit through an assortment of adverts actively and aggressively promoting a set of values and myths that I find mostly incomprehensible or alien.

They are myths about the happiness that comes from acquiring various consumer goods, values illustrated in sophisticated (and eye-wateringly expensive) bits of film that nurse some of our most childish fantasies about power and success.

As a cinemagoer, I’m being carefully targeted for conversion to a philosophy of life. If I don’t like it, that’s my problem. After all, this philosophy of life is completely self-evident to the film-makers, and assumed to be acceptable and attractive to every sane citizen. So advertising our Christian history is not intruding dangerous propaganda into a neutral and benign space. It is competing with existing propaganda, existing philosophies and ideologies. No wonder it’s a challenge for some.

Those who can remember the Lord’s Prayer will recall that in addition to words of worship and aspiration related to God, it contains the hope that there will be food and well-being for all, that we may learn not to think all the time in terms of what is owed to us but of what we might do to release others from guilt and debt; and that we may not be tested by life beyond what we can bear.

Yes, it encodes a philosophy of life — one that a lot of us would still find understandable and might even wish we could live by a bit more consistently. It is a philosophy shaped by the conviction that we are most human when least obsessed with defending and promoting our self-interest and when recognising our shared human needs.

It’s a philosophy rooted in the story that begins at the first Christmas, the story of a human life in which unlimited generosity and mercy were at work. It is not the product of Enlightenment reasonableness or modern scientific research. It’s there, as a vision of what humans might be, because of this very specific story. And whether or not you take on board what Christians would regard as the full implications of that story, it helps quite a bit to acknowledge that it was, and is, a perspective on life that didn’t just come from nowhere. We learned it; and we learned it from this history, this tradition.

Ah, but the trouble is that we all know what a great evil religion has been in human history, and how all the major conflicts of today’s world have their roots in religious controversy. Religion has fostered cruelty, obsession with power, inhuman repression, exploitation, dishonesty and misery. We tend to forget that much the same is true of politics, capitalism, socialism, science, alcohol, sex and football. None of these seems to be a rival candidate for being excluded from the public eye. And that’s largely because we know they all have also fostered joy, intellectual or imaginative excitement and a sense that the world could be better and fuller. Just like religion, in fact.

But we are so easily persuaded to panic about religion and to expect the worst. Because religious fanaticism is so much more visible now than it has been for a long time, we can assume that any and every expression of religion in the public sphere is a cause for anxiety. Visible religious commitment means we are instantly at risk of being manipulated subtly in the direction of horrific “medieval” tyranny and irrationality (incidentally, it would be nice if people stopped using “medieval” as a word of abuse: the Middle Ages, for Muslims, Jews and Christians, was a period of conflict and superstition, certainly — but also of complex and exciting argument, immense artistic vigour and intellectual diversity).

Every vicar is really a mad jihadist in mufti. And because it is so degrading for anyone to be made aware that quite a few of their fellow citizens share quite strong convictions about the moral world, we do all we can to avoid this painful embarrassment.

In one university I’ve encountered (not the one where I work, thank goodness), a friend involved in pastoral and counselling work was firmly and expressly told — in pursuance of the Government’s Prevent strategy — that it was unacceptable to express any opinion to a student.

This is asinine. Fanaticism is real and nightmarish, and if we can’t tell the difference between sane and mad religion, we have lost a significant skill. Equally, if we treat one another as infants who can’t cope with actual disagreement about cultural and moral matters, we do no one any favours.

The happy result of the ban on the Lord’s Prayer advert has been, predictably, that an impressively large number of people have watched it online. It’s an ill wind. But the fact of the ban brings into focus one of the least sensible and helpful aspects of the way a lot of people today think about religion.

Such people forget what religion — specifically Christian religion — has made possible, despite its historical failures and scandals. And they nurse the dangerous illusion that the values of a majority (or rather the values of the feverish and prosperous minority who dictate what we have to watch before Spectre or Carol begins) are the right ones, never to be challenged.

Christmas, 2,000 years ago and now, is a moment for the startling recognition that things don’t have to be the way they currently are and that something else may be possible. Things such as peace and goodwill, to coin a phrase.

Dr Rowan Williams is Master of Magdalene College, Cambridge, and the former Archbishop of Canterbury.