Something big, round and heavy fell with a clang in Times Square on New Year's Eve, and it wasn't the ball on the flagpole. Cee Lo Green sang a version of Imagine in which he changed John Lennon's lyric "and no religion, too" to "and all religion is true".

Outraged Lennon fans didn't need to use 132 of their Twitter characters to tell Cee Lo what they thought of him. On the other hand, perhaps they were just reminding him of his most infamous song title.

Among the New Year's Day tweets, I imagine there were one or two that said, in effect, don't you think you're taking postmodernism a bit far? To which Cee Lo responded: "Yo I meant no disrespect by changing the lyric guys! I was trying to say a world were u could believe what u wanted that's all."

Things really started to get bizarre when the fans accused him of blasphemy and sacrilege. "We do not take kindly to blasphemers like Mr Green. He must be boiled in oil for his apostasy!" Woah! First of all, the punishment for apostasy is, of course, stoning. Second, aren't we taking things a bit too seriously here? Is Imagine a sacred text?

This is yet another sign of what happens when people abandon formal religion. GK Chesterton gets quoted more than he gets read these days, but he anticipated the present age: "It is often supposed that when people stop believing in God, they believe in nothing. Alas, it is worse than that. When they stop believing in God, they believe in anything."

It is a natural human tendency to seek after meaning. The danger comes when people invest more meaning in objects, concepts, heroes, than those things can bear. At least the old religions have a series of checks and balances: traditions, texts, holy custodians who can tell you if you're making a prat of yourself – though they're not always listened to. So it's worth spelling it out: John Lennon is not God (and yes, I know about Clapton).

I want to be fair, though, so I think myself back to my impressionable, moody, atheist, teenage years (Leonard Cohen – when did he start getting so cheerful?). I was a late fan, admiring Lennon for his stripping away of all his former Beatles psychedelia, as in the modestly titled God ("I don't believe in Bible … Jesus … Elvis … Beatles"). But even then, I'm pretty sure I thought Imagine was tosh: new Lennon undermined by his old wishy-washy, druggy self. I've watched, bemused, as the song has been adopted as some sort of anthem for that generation: rated the second-greatest pop song after Bohemian Rhapsody. At least Queen knew they were writing bollocks.

One tiny irony: in the years since 1971, when the song first appeared, academic theology has filtered down to the street, dismantling the religious imagery used by Lennon. Thus, if Cee Lo wanted to be consistently religious, he would have sung "Some form of hell below us, but only in the sense of separation from God, above more than sky, but in a metaphorical sense, obviously." This is not the same as saying Lennon was right: just that the straw men he was knocking down no longer exist.

As for Cee Lo, there is a sense in which he has done John a favour. However fatuous we all were in the 1970s, he has managed to show that the 21st century can take fatuousness to a new level. "All religion is true" is like saying "All music is good", "All sport is interesting": the only thing you prove by making such sweeping statements is that you know sod all about the subject.