We tend to wish people a happy Christmas in Britain as a cultural nicety without checking whether the person we're addressing actually celebrates Christmas. There are plenty of people who won't be doing anything special on 25 December, whether for cultural, ideological or economic reasons, but I am not aware of anyone, from any background, who takes offence at this offhand, heartfelt well-wishing. Christmas is, after all, no longer regarded by the majority of our mostly non-religious society as a religious festival, but rather as a public holiday when we get together with our nearest and dearest to exchange gifts, squabble, eat too much and watch Miracle on 34th Street again.

I wonder, though, how many people have not been prepared for Christmas this year because of their conviction that the world would end last Friday, as predicted by the Mayan calendar. You scoff, but there will have been a few. The majority of people happily ridicule as superstitious nonsense the notion that aliens from Planet X were going to land on Mount Rtanj deep in the Carpathian range in Serbia (I kid you not: it's on the internet). Most, however, still regard it as unnacceptable to similarly dismiss the 2,000-year-old belief system of millions of Christians.

So what is the distinction? When does a cult become a religion? Is it not simply a case of how long a belief system has been around, allowing enough time for both its mythology and the man-made rules that house it to evolve and mature into a cultural identity. Should I not be free to afford the same respect or irreverence to followers of obscure UFO cults as I do for believers in the established organised religions? Maybe that is what living in a truly open and free society means. The truth is, I am more respectful of the beliefs of followers of the large organised religions, partly because it is not in my nature to offend and partly because it is still a taboo in our society not to.

It would be nice to think that there will come a day when the human race can run its affairs based on shared values of reason, decency, tolerance, empathy, respect and hope without the added baggage of religions or mythologies to justify or enforce them. But that day is far in the future. Until then, we can at least push for a more secular state. That need not mean a godless society, but simply an open one in which everyone is free to believe whatever they want – be they religious, non-religious or anti-religious – and not to force those beliefs on others, but to respect each other's right to hold their own views. Crucially, a secular state is one in which no religious group can dictate the running of government or be endowed with special privileges in law or policy.

Most importantly, living in a secular state should never mean one that is bland and homogeneous. Certainly, it should be one in which those of us who wish to can still celebrate Christmas. For me, this is as good a time as any to remember all that is positive about humanity, not because we seek the reward of eternal life or because we fear the punishment of a supernatural being, but simply because we want to. There were winter festivals of hope long before there was Christianity. "Christmas" is just the name we have given, in our culture, to what has been traditionally a universal human time of celebration across the world.

Just as we don't need God to be good, we don't need God as a reason to celebrate on 25 December. So, happy Christmas everyone, whether you are commemorating the birth of Jesus or simply celebrating the fact that you and I are here because of a wonderful sequence of highly improbable accidents, all obeying the laws of nature, and so we really should try to make the most of it. Now is as good a time as any to share that with all the family and friends who make it all worthwhile – especially since the world didn't end on Friday.