All my life I have looked on Christmas as a celebration that united people. Even if it only amounted to a lighted tree in a window, presents and a family dinner, it was something that made everyone happy. The fact that, in my part of the world, it was the start of the long summer holidays certainly helped to put people in a relaxed and expansive mood, but it was the magic of Christmas itself that seemed to make people smile and greet perfect strangers.

Of course, there were exceptions: loners and drifters always stood out more at Christmas, and still do, disturbing any feelings of smug well-being and reminding us to open the family circle to the elderly neighbour or the new immigrant and give of ourselves. But there was no sign that people of others faiths were offended by the Christian character of the festival. I never heard that the Jewish community might be unhappy or that Chinese and Indian shopkeepers might regard the holiday as an imposition.

Until recently. Distant rumblings of a culture war over Christmas finally reached our shores early this month as a clear salvo in the form of a card to householders from the New Zealand postal service wishing us "Happy holidays". Perhaps they have done it before and I didn't notice, but I was alerted this year by the sparks flying in the United States over this substitute for "Merry Christmas", which has featured prominently in news bulletins from my usual sources.

Generic "Seasons greetings" and the like are not new. Apparently President Kennedy started it for a portion of his Christmas card list at the White House in 1962 and in recent years even President George W Bush has been wishing everyone "Happy Holidays". This was controversial. But with national retail chains like Wal-Mart and Target following the trend, some Christian groups believe they are witnessing a veritable "war on Christmas" and have been returning fire. Boycotts have proved an effective weapon, bringing Target and Sears stores back to "Merry Christmas".

"This is a nation where surveys show 96 per cent of the population celebrates Christmas,” says Robert Knight, director of the Culture and Family Institute of Concerned Women for America. "There is no survey showing that people of other faiths are insulted when the majority celebrate Christmas or wish anyone a 'Merry Christmas'."

Yet there is no denying that things have changed in countries of the once-Christian West. Globalisation and large-scale immigration from non-Christian parts of the world do constitute a challenge in view of the long-term secularisation of Europe, North America and Australasia. Where Christmas often seems at best a family get-together, and at worst an excuse for a spending spree, excessive feasting and subsequent torpor, who really minds if no longer masquerades in public as a Christian festival?

After all, there would be nothing to stop Christians privately making as much ado as they wish about the birth of the Saviour. They could celebrate their feasts in their communities just like Jews and Muslims and Hindus and all the others. They might even be given some public space in which to do so, like the others, and the media could write nice feature articles on the interesting rituals of the Christian community around December 25, or Easter or any other time. A totally secular public establishment could bestow tolerant attention on all alike.

But some questions arise about this secular utopia.

In the first place, what other culture has followed this path or is likely to? The religious minorities for whose sake we are to abandon Christmas can all look to parts of the world where their religion is an integral part of public life. Some even come from theocracies where other religions, and secularism to boot, have few or no rights. This is not what Christians in the West want, but are they to be the only ones with no country, only toleration?

Secondly, what would a Western nation celebrate apart from religion? The American Thanksgiving Day would be out because it was instigated by Christians (thanksgiving to whom?) and so would anything similar. That leaves independence days, royal anniversaries, war memorials and labour days – none of which are entirely free from controversy these days. In my country we struggle to make our national day – marking the signing of a treaty between the British Crown and the indigenous Maori tribes – a celebration of unity. It is hard to agree on what it represents apart from an extra day at the beach.

Which brings me to a third question: Can holidays themselves unite us happily as a nation? Everyone enjoys a holiday, so perhaps the "Happy Holidays" people are onto something. It's true that not everyone has the same amount of holidays around Christmas and some have to work right through, but hey, everyone can enter into the holiday spirit.

Hmmm. The holiday spirit: rest, relaxation, family togetherness, friendship. These are all good and necessary things which can bring pleasure and dispose people towards greater solidarity with their countrymen. But enough people already depend on the "holiday spirit" – more or less living for the next holiday – for us to see what effect it has on individual happiness and social cohesion, and the signs are not positive. Nations are less united than formerly and individuals suffer more mental illness than ever.

The truth is that we human beings need more than holidays to make us happy. We need a sense of purpose in life which can only come from a sense of its meaning. This is what religions do. The monotheistic religions, at least, teach us that our lives are not an endless cycle of work and holidays, but that they are going somewhere – and, what is more, to Someone. And that Someone motivates us to live well, respecting others, even though we do not always live up to his demands.

Nothing is as persuasive in this regard as Christmas – the festival of God who became a baby and was born in a cave in order to win the love of his creatures. It may be true that many in the West no longer appreciate that the light on their Christmas tree comes originally from the stable, or that the joy and hope it stirs in them could not exist without Christ. But then again, many do still have an inkling that is the case, precisely because the celebration still publicly bears his name. Take that away and soon the celebration itself will go, along with the special lightness and human warmth that it brings.

In that case, people of other religions and none would have more and not less reason to resent the dominant culture of the West. If they think Christians behave badly now, when they still celebrate their religious roots to some degree, that behaviour is nothing to what they will see in a future where all public reminders of the Christian Lord and his gospel are wiped out. The rest of society needs Christmas as much as Christians do.

Carolyn Moynihan is Deputy Editor of MercatorNet. She writes from Auckland, New Zealand.