First the nuptials, then the killing. Don't tell me it was just coincidence.

Don't tell me that Osama bin Laden wasn't caught unawares while he was watching a recording of the royal wedding for the umpteenth time. We can speculate as to the moment when his defences would have been at their lowest – was it seeing that dress, was it Harry's joking aside to William, was it the singing of "Jerusalem", was it the moment the Queen left the Abbey? – but that his instinctive reverence for royalty was what did for him, only a fool would question. My own bet is that it was the kiss on the balcony that sealed his fate. He'd have heard the helicopter, the whispering, the rope ladders being lowered on to the roof of his compound, and known his hour was upon him, but until he'd seen that kiss one more time he was unable to move from the box.

Thus will sentimentality be the undoing of us all. Funny, because my friends and I had been joking about it only a couple of days before, while we were waiting for the kiss ourselves. The whole world was watching, Huw Edwards had reminded us in tones calculated to make the whole world get up and do something else. So we tried imagining the whole world watching, and that included Bin Laden in his cave high in the Tora Bora, fiddling furiously with the satellite dish for his field telly. What would he have made of Posh Spice, we wondered, who turned up for the wedding with her satellite dish on her forehead. And would he too have fancied the bride's sister in her sinuous white frock?

So the joke's on us, and even more on those for whom it has been a source of immense satisfaction that an unaccommodated man sitting in the dirt, with only mountain goats for company could outwit the technological and military might of the United States. Now we discover that all along he'd been living the life of Riley, with a feather bed to sleep on and at least one wife to keep him warm. Part of the myth of Bin Laden's invincibility, not to mention, for haters of America, the soundness of his moral purpose, was the rusticity of his existence. The mud, the mud – how the politically simplistic long to return us to the mud. So the fact of Osama's having declined the mud himself is a matter of more than incidental irony.

The nuptials and the terrorist – how wonderfully each illuminates the other. Osama bin Laden was the ultimate ideological being: unshakeable in his convictions, convinced he knew the difference between good and evil, a man driven to mass murder by the pure single-mindedness of his vision. Whereas the thousands who watched the royal wedding didn't have a clue what their motivation was or what they believed or what cause they were serving – they just watched. In the days since the wedding, more words than there were watchers have been expended trying to explain what happened, what the event and our response to it tell us about the nation, about the constituent parts of our society, about chavs, about the upper classes (is it getting harder to tell the one from the other?), about the monarchy, about the institution of marriage, about the church even. May I venture an opinion? It tells us nothing except that we have a genius for not knowing why we do things, for acting out of beliefs we don't have, for behaving in ways that do not serve our best interests (not least because we don't know what our best interests are), for confounding our own intentions – in other words for being entirely illogical and purposeless. Discovering such illogicality and purposelessness in themselves the other day, commentators (a number of them republicans) scratched their heads and marvelled not only that they watched a wedding about which they thought they had no curiosity – to which, indeed, they had a strong ideological aversion – but that they actually enjoyed it.

Is it permissible to enjoy that which you abhor? Reader, it is. Enjoying what you abhor, abhorring what you enjoy, not knowing what you think about anything but doing it anyway – this is what stops us being Osama bin Laden. What republicans have been bemused to discover about themselves is nothing more nor less than that they are human. In their befuddlement, republicans remind me of atheists. Each assumes that if you are not him, you must be his opposite. If I am not a republican I must be a royalist. No, I mustn't. If I am not an atheist I must be a believer. No, I mustn't. I needn't be anything. The rationalist view of human purpose, to which all atheists if not all republicans are wedded, misses the best thing about us, which is that often we do things for no good reason and for which there is no genetic payoff, unless benign pointlessness is a genetic payoff.

Myself, I can't imagine why anyone would spend the night in a sleeping bag, far from those amenities which alone make physical life bearable – one shower, two lavatories, three bars of soap, a four-poster bed and a five-star restaurant – in order to see a coach go by in the morning. Osama bin Laden wasn't prepared to undergo such discomfort. A devotion to the institution of monarchy doesn't account for it, because people will just as soon queue all night to buy a new Harry Potter, the latest iPad, or a T-shirt from Abercrombie & Fitch. Nothing explains it. Not need, not greed, not communality (which you can get indoors), not even insanity.

In the same way nothing explains the impulse to wave a flag. Wave a flag and you mortgage your humanity to mechanism. So why do it? For the same reason, I believe, that we join in a Mexican wave or hold up squares of cardboard during cricket matches which say 4 or 6 or NOT OUT! and show them to the television cameras. Not because we are patriots or royalists or cricketists or Zapatistas, but because – good-naturedly – we don't know why we do anything.

I am not surprised that atheists and republicans despair of those they would save from what looks to them like irrational behaviour. But they make the mistake of assuming that those who don't think as they do must think erroneously, when the truth is they don't think at all. The world might be better if they did, but it could also be far worse. Remember Osama bin Laden who knew exactly what he thought.