Howard Jacobson: We'd already shown Megrahi compassion – by not sentencing him to death

The criminal we do not hang must serve the life sentence that is hanging’s substitute

America doesn't love us any more. And frankly I don't blame her. We aren't worth loving. We look bloody awful, for a start – wet, blowsy, littered. We don't keep our word. And we are bad company – low on conversation and out of big ideas. (Opening up Libya to BP is not a big idea.) So it's no wonder we've been dumped.

There is irony in this. We thought the romance was just beginning. Obama was our soul mate. He would undo all George Bush's evils, pull out troops from Afghanistan and Iraq, hand Israel over to Hamas, and together, hand in hand, we'd make the world a safer, greener place. The moral infants that we are.

The latest falling out – and it is more than a lovers' tiff – is over the release of the Lockerbie bomber. Pushed back on to the defensive, we scramble for the ethical high ground and adopt our usual scoundrelly tone of high, hurt Christian sanctimony. Why, we have done no more than exercise that most civilised of virtues – compassion. There is blackmail in the word compassion: it makes an animal of whoever, for whatever reason, chooses to withhold it or call it by another name. We are moral infants politically, and we are moral infants morally. We think that saying we are virtuous makes us virtuous.

The idea of BP lobbying Jack Straw to throw Megrahi's release into the diplomatic mix is enough to make the angels weep. But let's leave greed out of it for a moment. Whatever the secret deals – and Brown insults us profoundly if he thinks we'll accept that a deal is not a deal until it's called a deal – one of the most obscene aspects of this pusillanimous affair has been the automatic assumption of righteousness by those who, out of whatever motive, have trumpeted the virtues of compassion, as though compassion is itself an open-and-shut case. It is still to be proved that a person who refuses "compassion" to those who murder with their eyes wide open is less ethically refined than one who employs the term without discrimination or understanding of its implications, and without regard, as well, for the wider suffering it might cause and the breaches of trust it might entail.

Virtue, reader, never was a simple matter.

Of those who claim their trust has been breached in this instance, the Americans have a mighty strong case – having been party to an understanding that Megrahi would serve out his sentence in Scotland – and the families of the victims a stronger one still. Ask what compassion has been shown to them in the act of showing it to Megrahi and you only begin to enter the complexities of exercising mercy where blood has been shed. But every single one of us, whether American, Scottish or English, whether related to a victim or not, has good reason to feel betrayed. A judiciary acts on our behalf. Let it argue that it stands for the better part of us, that its impersonality raises it beyond those passions which prevent our judging clearly and passing sentence calmly, the fact remains that it is subject, as are we, to a contract in which we submit our will on the understanding that it will speak fairly for our grievance.

Several writers of letters to this paper have applauded showing compassion to Megrahi, arguing that the feelings of the victims' relatives are irrelevant – a position which merely sacrifices one act of compassion to another, and is the more perverse for favouring the guilty over the innocent. Perverse is the kind word for it. Soul-sickness is what we are actually dealing with here, a hankering to press one's lips to sin. But even leaving such soul-sickness aside, it is simply incorrect that the showing of compassion is the judicial system's prerogative and none of anybody else's business. In an irresistibly furious article in this newspaper last week the distinguished human rights lawyer Geoffrey Robertson QC – no hanger and flogger himself – made the point that we already show compassion to those who themselves have shown none "by abjuring torture and the death penalty".

This, in my view, is the argument that knocks out all others. Compassion is built into our system. We already showed it when we did not do to Megrahi what many would have liked to do, and many must now wish we had done, and what there will always be a residual argument in the name of natural justice to say we should do. We forgo the exaction of revenge at great cost to ourselves; it does violence to our sense of redress and retribution to let a person live who has wilfully taken one life, let alone a hundred.

The history of humanity is still to be written and we cannot know how the judicial kindness we show to brutes in our enlightened times will be judged, whether from the point of view of social efficacy, from the point of view of ethics, or with regard to the well-being of our souls. I'd be surprised if we weren't judged leniently for it, but it is possible we will show as demented fools who denied ourselves the satisfaction of a justice it is in the end impossible to live without. But at least, if vigilantism must be forsworn, let the system keep its side of the bargain.

If you are not yourself outraged by mass murder, then you are not. It falls to you merely to step aside. You are not at liberty to condemn those whose outrage cannot be set at rest. The judicial sytem, too, must take account of the ravages of loss and impotence, no matter that it exists to rise above them. It is part of the contract which the outraged and the judicial are meant to enjoy, that the latter doesn't compound one pain with another.

We rightly expect, when we leave our weapons at the door, that in return a proper punishment will be exacted. The criminal we do not hang from a tree must serve the life sentence which is hanging's substitute. We do not forgo our rage only to see him released when he is not feeling well. And if we do forgo our rage for that, then where at last will our rage go? The Furies cannot be wished away.

Once again, the moral life has been hijacked by criminals and simpletons. It was a spiritual indecency to show a compassion to Megrahi of which he was already the recipient. Fed, on top, by lies and subterfuge, by cynicism and avarice, it violated the humanity in whose name it was enacted. And if we don't see that then we deserve to lose our friends.