The other is when they complain, at this time of year, that we're "forgetting the true meaning of Christmas". (And this year they're enjoying a mega- grumble as we forget the true meaning of the Millennium as well). Well I have, as they would say, good news.
The whole point of religion is to be so supple and flexible that it can fit any ideology. That's why every general, in every war, can claim that God is on their side. There is no case, as far as I know, of a general saying to his troops "Last night I prayed to God in this, our hour of need, and he answered me in his prayers, and, well, unfortunately it seems he's backing the Turks on this one."
There was even a member of the Christian sect, the Ranters, after the English Civil War, who claimed that God had told him personally to break all 10 of the commandments. Which must have ended with them going round knocking on doors and asking "Here, you haven't got an ox I could covet, have you?"
This flexibility arises because religious ideas are not formed by divine speeches to men on mountains, but by human beings as a response to their earthly aspirations. The most plausible theory I've heard about the origins of Christianity is that it began as a radical movement among labourers and dispossessed small farmers as a focus of opposition to the Roman Empire. This, it seems to me, is more likely than loads of Middle-Eastern peasants suddenly thinking, "I don't know why, but as from today I no longer believe that Mars is the God of War. Instead I feel that God is actually comprised of a holy trinity, including his son, who's that long-haired bloke who keeps wandering around the wilderness".
Then as a religion spreads, every new convert finds something in its teachings that justifies their own behaviour. Even the most awkward passages in the Bible got brushed aside, as the church admitted rich men, saying things like "ah, but what you have to remember, is that in those days they had enormous needles, and camels were only half an inch long."
So, some of the greatest heroes, as well as the most appalling tyrants of history, have claimed they received their inspiration from God. Margaret Thatcher is a Christian, probably assuming that the feeding of the thousands was proof that if enough bread is created, some of the loaves will "trickle down" to the starving. And Tony Blair, the Prime Minister, is a Christian.
Which seems strange, seeing as how he led the abolition of Clause Four of Labour's constitution, on the grounds that it was way out-of-date for being written (by Sidney Webb) back in 1918. When does Mr Blair think the New Testament was written? Perhaps he thinks it was knocked up by Alistair Campbell at a cocktail party in 1992.
And yet the church has led the most courageous opposition to South American dictators, and to racism in the United States. Such contradictions of Christianity appear in some of the letters that I've received, following my successful plea to stop Cliff Richard having the Christmas number one record (God bless that boy band).
One starts "from a well-wisher", and ends eight lines later "Hands off God's word. No one resists God and comes out unscathed."
I had no idea that God was an East End villain, or that his disciples used language and tactics developed in the pubs of Bethnal Green in the Sixties. Poor George Michael was even ruder about Cliff's record than I was. He'll probably get a visit from two blokes in dark glasses, carrying Gideon's Bibles, saying "tell you what, nice mansion you've got here George. Be a terrible shame if it was knocked down by some sort of - let's say - thunderbolt".
So as well as loving thy neighbour, the true Christian meaning of Christmas can be found alive and thriving in every moment of commercialism, greed, and gluttony that the festive season brings. Their religion has managed to accommodate concepts more indulgent than rampant profiteering and stuffing your face.
So the character I feel really sorry for this Christmas is not God, but Santa. The World Trade Organisation must be plotting right now against this flagrant undermining of free trade, dishing out free presents with not a thought for how he's depressing the market-value of the toy industry.
And if they want to write any more letters encouraging a truly Christian spirit to the Millennium, they should write to Tony Blair. For he's the biggest fan of the Millennium Dome, financed by businesses eager for advertising and a healthy financial return.
As a Christian himself, they could point out, surely he should begin the new Millennium by strolling into the temple of the Dome and kicking out the moneylenders.