So that was all it took – one year, one little year for him to go from Superman to Anti-Christ. We took longer changing our minds about Blair. We take longer doing everything in this country. But essentially it's the same story: a grotesque over-investment of faith and trust followed by a grotesque under-investment of faith and trust, the one following the other as surely as the pendulum that swings to the left will swing to the right.

Wisdom has it that it's moderate middle America that's deserted Obama, but I see little that's moderate in the spirit of its defection – Hitler moustaches, invocations of Russia under Stalin, or worse, Britain under the National Health. There was nothing moderate, either, about the chant of 'Bliar!' that went up in our streets before the Blair ceded authority to the Brown, though there again I read that it was the people speaking. Maybe it's time to accept that the people or whatever other name we give them – Middle Anywhere – is never moderate. They adore or they abhor, and if they can abhor someone they once adored they are in heaven.

I must stop saying "they". We are all in this. We lack ambiguity. Which is to say we lack a sense of tragedy, for it is tragedy that asks us to face up to the essential irreconcilability of things. We want right or wrong, good or evil, but except in very rare instances, there are no such absolutes. Humanity is tossed between the two, just as nature shows us now a face of the utmost serenity, and the next is pitiless in its destructiveness. Which is the true face of nature: dusk in an English country graveyard, where drowsy tinklings lull the distant folds, or the hell of Haiti? Neither. Both.

And as with nature so with man and the efforts he makes to understand a contradictory universe. The rationalist scorns the metaphysician, the mystic shakes his head over the scientist, as though only one of them can be right and must cancel out the other. I have recently been making a film about the book of Genesis. Friends worry I am turning religious. I am not. Unless I always was religious, which I wasn't, but then again does it behove a novelist to state categorically that he does not believe when belief is among the subjects he is as like as not going to address? Can you write about a man who believes, if you think he is a fool? Can you write about a man who does not believe if you don't have an instinct for the clear-eyed scepticism that drives him to atheism? And another, prior, deeper question: isn't the impulse to create akin, in some way, to the impulse to believe, so long as the impulse to believe is shot through with uncertainty and doubt?

I hope the film I've made is ambiguous in its argumentativeness. Nothing spoils a good argument, wrote the Spanish poet and philosopher Miguel de Unamuno, like a fool who knows what he's talking about. Unamuno is famous for writing The Tragic Sense of Life. A tragic sense of life precludes the folly of certainty. Which is why you aren't going to find it in politics or popular polemics, the prime site of which today, of course, is the internet with its raging labyrinth of twitter chambers, each one a little Bedlam of aggressive sureness. Ricky Gervais, I learn, has just quit Twitter, arguing that "there is a certain lack of dignity for adults who use it". Well what do you expect from something that calls itself Twitter? You should no more expect to encounter dignity in Twitter than decorum in Club Oops.

This, though, hasn't stopped a well-known general twitterer by the name of Sunny Hundal from writing in defence of his habit. What critics of the "Twitter-Mob" don't seem to understand, he says, "is that these are real people ... trying to do something about the world around them". Well, you won't hear a word against "real people" in this column. Indeed, in so far as we have a preference, we prefer real to unreal people any day.

But the argument against the bulk of twitter sites, in whatever form the internet facilitates them, is not that the participants don't care about the world around them but that they are too angry, often too incoherent and inarticulate, and too lacking in a sense of the tragic, to make the slightest sense of it. You can always tell when someone's tragic sense is faulty: he turns abusive. Sunny Hundal describes one journalist's defence of another, in the face of a concerted twitter attack, as "piss-poor". Not a persuasive argument, piss-poor, but then persuasion isn't the name of the game. Abuse is the name of the game. You Bliar, Blair. You Socialist, Obama. You twat, whatever your name is. God, maybe. You twat, God!

Sunny Hundal cites approvingly a fellow-twitterer called Anton Vowl, if that's his real name and not just an anagram of Wanton Lov. I went in search of one of his postings, another defence of the craft of twittering as practised – yes, you've guessed it – by "real people, who think for themselves". It contains a warning to journalists (ie not real people) that if lots of twitterers are "saying you stink ... it could just be because you stink".

Now just as we are for real people in this column, so are we for lively disputatiousness and witty badinage. But telling people they "stink" belongs to neither category. Nor does calling them an "arse" (Anton Vowl) or delineating their work as "cobblers" (Anton Vowl).

Forget the inelegance, it's the intellectual laziness we should be concerned about, the confidence that it will pass muster as serious comment in this most idle of media, where mere opinion mistakes itself for thought, and mere disagreement poses as judgement. Ambiguity? In the twittersphere? Not a chance. Here, no distinction is made between modes of discourse: nothing on which you pronounce is ever teasing, ironic, tentative or experimental; everything is a statement of brute conviction against which you measure your own. The man for whom life is tragic accepts there may be wisdom in views which do not tally with his, doubts the value of "views" altogether, and takes pleasure in knowing that there are people of substance – religious men and atheists, the godly and the ungodly – with whom he will never see eye to eye. The clown holds that everyone who doesn't believe what he believes is a wanker or an arse.

'The Bible: A History, Part 1 – Creation', written and presented by Howard Jacobson, is on Channel 4 tomorrow at 7pm