If a divorce happens before children are involved, there may be no greater carnage than any boy-girl split-up. But feed children into the equation and the whole thing is much more hellish because, as everybody knows, it damages the kids. But is it really that simple: it's better to stay together for the sake of the kids?
What seems undeniable is that children whose parents divorced are on average about twice as likely as those in intact families to have a whole lot of problems: aggression, insecure friendships, unpopularity at school, lower IQs, academic underperformance, disharmonious and divorce-prone adult relationships themselves, and so on. However, by no means does that mean staying together is invariably best.
For decades the debate has raged as to whether it is the divorce as such which is the problem, or the cluster of associated misfortunes - the disharmony before and after fissure, the absence of a loved parent, the halving of the household income of the mother, the distress caused to her by the break-up.
Through the scientific fog emerges one clear message: it certainly can be a whole lot worse for parents to stay together if they are grossly disharmonious or if one of them is very dysfunctional.
For instance, sons with very antisocial dads are more badly behaved if he lives with them than if he doesn't. In such cases, it's best for the boy if the dad does a bunk - unless you are trying to breed a criminal. But most telling of all, children from intact homes where there are high levels of rancour and conflict are as likely to be delinquent as ones from broken homes - marital or relationship status is not the key issue.
A strong proof of the importance of what happens after the break-up is whether it is Mum or Dad who is left holding the babies. When it's the mother who has gone, leaving the dad in charge, the outcome is dire. Over half of sons in this scenario will be delinquent children and a staggering two-thirds of cases will acquire an adult criminal conviction - twice the proportion than if it's the dad who leaves the home.
There are some outcomes which at first sight seem to be affected by divorce alone. On average, a daughter whose dad left the family before she was 10 comes into puberty six months earlier than one from an intact home - bad news because early puberty increases the risk of early sex, teen pregnancy and school failure.
But daughters of intact parents who are not close to their dad also come into puberty earlier.
All in all, the damage done by failed marriages seems to be cumulative. Witnessing a lot of crockery flying or tense atmospheres is jolly bad for children, putting them at much greater risk of disharmonious relationships themselves. But so is having a beloved parent disappear from your life.
Next week: I had that Tony Blair in the back of my cab...
· Oliver James is unable to enter into any personal correspondence.