Howard Jacobson: The first step on the road to wisdom is admitting that you don't know anything

It is beyond us to balance fairly the rights of an unborn child against those of the mother

Remember Keats's "negative capability ... being in uncertainties, mysteries, doubts"? Whatever happened to that? Now everyone is sure about everything – when a foetus becomes a person, the rights and wrongs of simulating life, how little or how much a child has to gain from looking into the eyes of a father. Verily I say unto you, not Solomon in all his wisdom was as puffed with the vain conceit of certainty as we are ...

Among the humiliations that lie cringing in the cellar room of my memory is a period teaching in a school in Sunshine,a largely immigrant suburb of Melbourne, built on a volcanic plain of suffocating heat. I wasn't cut out for schoolteaching. Too impatient with the young for being young. And I am bolshily elitist with them. They read The Waste Land or they stay home. I stand by the principle – give everyone the best – but it was bound to hit snags in a school where the majority of pupils came from Yugoslavia, barely spoke English, and knew their future lay in working in a munitions factory in which case what use The Waste Land. Every use, of course, but it's hard to get that one across.

In Sunshine teachers don't wear gowns or expect to be addressed as "Sir". But I'm the product of an English grammar school and know how a teacher should comport himself. My pupils mutinied the minute I swept in to class. "Don't know," they answered in unison to every question I asked. "Done your homework?" "Don't know, sir." "Why don't you know?" "Don't know, sir." "How long do you intend going on with this?" "Don't know, sir."

"Then burn in hell," I should have said. Somewhat redundantly, since the fires of hell had already half consumed them.

I lasted two weeks. What finished me was a class of overaged girls from Sremska Mitrovica dancing on their desks with their skirts raised to their waists, chanting "Neznalica!" which, since nescient means ignorant, must mean ignoramus, but whether that was them or me I didn't stay to find out. I fled the school with my gown flying behind me like Billy Bunter's housemaster chasing him around the quadrangles of Greyfriars. From me they learnt precisely nothing; from them I learnt the unassuming wisdom of saying you don't know when you don't.

And we don't. We don't know and we won't ever know what a foetus feels at 20 days or 20 weeks. It is beyond us to balance fairly the rights of an unborn child against those of the mother bearing it. And not only the rights but the moral, social and psychological consequences of putting one before the other. I'm on the mother's side myself, but not because I know anything, merely because history makes me so.

I lived through the Sixties; there were pregnancies I had a stake in terminating. But I doubt whether that makes my reasoning ethical. And who's to know whether ethical judgements are of any use to us anyway, if it's happiness we're after. No happy life is possible that has not an admixture of cruelty and immorality in it. Nietzsche must have said that, and if he didn't, I'll say it for him. But I don't know it to be absolutely true. I simply feel it in my waters, and a man's waters are not to be confused with truth. Least of all in the matter of carrying children. And that's something else that feels like truth to me but might not be – that no man has a right to pronounce on the ethics of a woman's confinement. To popes and rabbis I have only this to say: You want every unborn child to live? You carry them.

But there has to be reciprocity. Much as she might like to, a woman cannot have a child by act of volition alone. So re-enter, stage left, man. A woman's body is not his business until he's called upon to father, but then it is. Or at least the consequence of his fathering is. I well understand why a woman might fall out of love with the man with whom she conceived her child, or not care to know him if their love never got further than a test tube; but that's a different thing from starting out wanting a child to be fatherless on principle. A child born only of woman is a delusion of ideology, a metaphor not an actuality, the child not a child but a quibble on the idea of conception.

So is that so wrong? How do I know? I just don't like it. But then I wouldn't. I'm a man. My seed is not to be quibbled with. Not that I'm one of those men who long to track down and benefit with moral influence the lost children of their youthful indiscretions. I am not patriarchally omnivorous. I would, though, quite like my mislaid offspring (were there any) to know what pulse it was that co-opted them into being. For their sake or for mine?

There you have me again. On whose behalf does the Human Fertilisation and Embryology Bill enact its wisdom? The gender-fastidious woman who doesn't want her child contaminated by so much as the idea of man, or the child whom it could reasonably be argued is bound to be the poorer – as we are all the poorer by every contrary influence we are denied – for missing out on the experience of a dad?

Do we know for sure, though, that children benefit from having a parent of each sex? My own view is that marriage is a symposium and the child thereof the richer by the amount of gender-disputation he gets to overhear. But there is ample evidence of children being reared successfully by single, divorced, or non-disputatious parents. Are the knife-carrying murder-children of today the consequence of broken homes, or the culture of crap they ingest from the streets, the telly, and schools where The Waste Land is never taught? You don't know, I don't know. Together we know nothing.

"MPs defy public opinion on abortion," screeches the Daily Mail, to which I answer, "Thank God for MPs." Parliament, for all its faults, at least debates. Public opinion merely opinionates. Only turn to those who speak their thoughts on the World Wide Web of Demos to see what anarchy and vitriol public opinion descends to when it rules unchecked. Every one of them his own conviction-crazed Dawkins of the blogosphere, a stranger to uncertainty, mystery or doubt. And every one of them, for that very reason, wrong.