I find it near unbelievable that anyone can propose sending foreign troops back into Lebanon, as in 1958, 1976, 1978 and 1982. The penultimate intervention, by the United Nations, was specifically to "restore international peace and security" and assist the Lebanese government in gaining "a monopoly" of authority along the frontier with Israel. It failed because neither side wanted it to succeed. The only settlements in the region have been a result of wars, whether with Jordan, Syria or Egypt. It is local people, the resolution of force on the ground, that will alone resolve the latest conflagration.

It has become a moral axiom of North Atlantic statesmanship that military potency confers a right and a duty to intervene. A subsidiary premise holds that such intervention will always be for the good. Hint that some conflict might be better resolved if the west stayed aloof and the cry goes up, "What would you do, then? You can't just do nothing."

To the feelgood fanatics of London and Washington, leftwing and rightwing alike, they must be the subject of every verb and the world its object. They are the children not so much of Palmerston and Disraeli as of the crusaders, the conquistadors and the Comintern, blessed with massive moral assurance. The idea of leaving wars to resolve themselves, states to find their own leaders and regions to evolve their own equilibrium is to them not just mistaken but immoral.

I once made a vow never to write about the Middle East. I had visited Israel and Jordan and was in Beirut in 1983 during an agony of foreign intervention comparable only to the miseries of modern Baghdad. I watched the cynicism with which western armies arrived after the televised horror of the Sabra and Shatila massacres. I watched the cynicism with which they left when the going got hot. My last image was of an American battleship lobbing shells into Chouf mountain villages to provide media "cover" for the US marines' retreat.

I realised that there was no way of calibrating comment on this subject that might inform debate rather than merely stir prejudice. Each side wanted not intelligence but support or condemnation. A sickening feature of every crisis was the eagerness of statesmen to "get engaged", as if the Middle East were a gymnasium in which to practise diplomatic exercises. Harold Wilson thought he could pacify the region. Lord Carrington was seeking a Middle East peace deal in 1982 while Argentina was invading the Falklands. Tony Blair naively traded "Middle East peace" for joining Bush in Iraq. Britain has claimed a role in every Oslo accord, every road map, every two-state solution, as if the Levant were somewhere in Northern Ireland.

Last week, Blair hamfistedly pleaded with George Bush to be allowed to play once more. The Commons chorus demanded visits, statements, exhortations. Sir Menzies Campbell called for "action to stop the escalating conflagration", as if peace on Earth could be ordered with club soda. We can all read Amos Oz, writing last week, and sympathise with his exasperation at peace moves by Israel being met with the shelling of settlements and the kidnapping of soldiers. We can all see the destruction of Beirut and killing of civilians and feel an equal and opposite sympathy. The terrorising of innocents is nowadays the small change of limited war. Yet how unfit for purpose is the language of sympathy. The morality of "something must be done" is weakened by being intransitive.

There are two strands to the current debate on intervention. One simply states a humanitarian obligation to show concern for those in pain, whatever the reason and whoever is to blame. From the foundation of the Red Cross on the battlefield of Solferino in 1859 to the aid effort expended on Ethiopia in the 1980s, citizens of rich countries have felt a duty towards those in distress.

Only since the end of the cold war has this duty been polluted by politics. In 1992, the Washington Post rewrote the UN charter to justify America's invasion of Somalia since the latter's government had "improperly treated" its own people and thereby sacrificed its territorial integrity. Intervention was converted into a moral duty by Blair's 1999 "humanitarian crusade" speech in Chicago. "We cannot turn our backs on conflicts and the violation of human rights ... if we want to be secure." Blair's confusion of humanity and security has bedevilled debate ever since. After 9/11 it opened the gate for generals and the military/ industrial complex to seize the initiative, with results that can be seen on the streets of Iraq today.

The idea that Britain (or any other country) enjoys a unique legitimacy in intervening in the affairs of sovereign states is legally doubtful and racially repugnant. Blair's thesis that any state that is not democratic is somehow a threat to Britain is absurd, as is the implication that a love of freedom cannot speak for itself but must be imposed by force of arms. Quite apart from the madness of this imperialism, the west cannot implement it. It can hold in thrall such puny neo-colonies as Kosovo, East Timor and Sierra Leone. But in Iraq it has failed and in Afghanistan it is failing. The idea of bringing similar bounty to Iran beggars the imagination.

Intervention has brought not peace but violence to these poor peoples. The mendacity of the neocons in claiming gains from intervention is equalled only by the enthusiasm of liberal supremacists to "finish the job". The humanitarian urge is time-honoured. It "does something" about human distress through charities and NGOs rather than governments and armies. Yet its steady morphing into the paranoid warmongering of western politicians is an international catastrophe. It is fuelling anti-west extremism and negating any humanitarian motive. What democratic cause can justify 1,000 deaths a week from "nation-building" in Iraq?

Of course something must be done about the agonies suffered by the people of the Middle East. Humanity demands it. I would sail the first Red Cross ship into Beirut harbour. But I would sink the first aircraft carrier.

simon.jenkins@theguardian.com