By Simon Jenkins

The foreign secretary speaks as part of a political generation with no experience of war and little sense of history

David Miliband loves democracy. We all love democracy. We also love capitalism, social welfare, child health, book learning and leatherback turtles. We would like the whole world to love them too, and we stand ready to persuade it so. But do we shoot anyone who refuses?

It is hardly credible that two centuries since Immanuel Kant wrestled with this oldest of ethical conundrums, a British government still cannot tell the difference between espousing a moral imperative and enforcing one.

Yesterday in Oxford the foreign secretary decided to update the 1998 Chicago speech of his then mentor, Tony Blair, in which Blair tore up the UN's sovereignty provisions in favour of the new "liberal interventionism". He proposed a doctrine of international community, which he claimed, like St Teresa, to have "witnessed". This required Britain to attack sovereign states unprovoked if this would end a violation of human rights.

Blair qualified his zeal with reference to military feasibility, a "readiness for long-term commitment" and "our national interest truly engaged". Like any interference in the lives of others, the motives were soon mixed and the language confused. How feasible is feasible? How long is long term? What is an "engaged" national interest: a moral crusade or an arms deal?

Nonetheless, as Kosovo and Sierra Leone were to show, Blair was right to acknowledge a humanitarian instinct beyond relieving the starving, as in Biafra or Ethiopia. In 1993 the liberal Washington Post was goading the US to invade Somalia, since states that "treat their peoples badly" should lose the protection of the UN charter's protection. Such unilateral rewriting ended in tears, but this did nothing to halt the exhilarating "virtues imperialism" of many on the left and right.

Miliband brushes aside the blundering into Iraq and Afghanistan as errors of implementation rather than principle and takes the Blair doctrine into new territory. He wants his pan-democratic world to be achieved by peaceful means, by trade, multilateral action and - his new soundbite - a "civilian surge".

Should soft power fail, Miliband wants to use sanctions and send in troops, for instance through offering security guarantees to regimes that "abide by democratic rules". Such measures would need to embrace internal and external security, and be of universal application if, as Kant warned, they are to go beyond opportunism and carry moral force. They would have guaranteed Dubcek's Czechoslovakia against the Soviet Union, and Allende's Chile against America. The regimes in Baghdad and Kabul would need guarantees indefinitely, as would an elected regime in Pakistan - guaranteeing it against insurgent Taliban and lurking generals.

Miliband calls any scepticism "a retreat into a world of realpolitik". Such point scoring may do for an Oxford debate but not for bereaved army mothers taking him to the high court, or the thousands of victims of his doctrine who see hard power interventionism as a menace to life and order. The professor of political science at Baghdad University said yesterday that the imprisonments under Saddam were more tolerable than the weekly murders, kidnappings, militia censorship and female repression his department is suffering. Is Miliband saying, from the comfort of his office, that this man is deluded?

Few would quarrel with the platitude that democracy is the least worst way of governing a freedom-loving state. But history shows that democracy takes centuries to bed down in any culture (including Europe's). This generation of western politicians has no experience of war and little sense of history. The new interventionism may differ from the old imperialism in not seeking to settle or rule countries. But it is the same in believing that western values can (and should) be imposed on often reluctant states through military occupation.

I regard the way I am governed as superior to most. But I am not so arrogant or naive as to believe I can change other states by persuasion or war. The latter is an infringement of self-determination and has proved starkly counterproductive. The greatest boost to the overrated Islamist threat is from just the power projection Miliband supports.

In the non-interventionist 1990s, the thinktank Freedom House charted a steady growth in democracy worldwide. With the advent of the democracy crusaders Blair and George Bush this trend has probably gone into reverse. The cynical appeasement of China and aggressive treatment of Russia and the Muslim world has done no service to democracy. Indeed the cause has fared better in south-east Asia and Latin America, where outside pressure has been least in evidence.

There is no text in international law that justifies ramming a system of government down the throats of others. Self-determination, warts and all, has been the defining essence of the nation-state throughout history, which is why the UN charter qualified it only in cases of cross-border aggression and humanitarian relief. The robustness of this doctrine is shown in half a century of relative peace worldwide. Collapsing it has been disastrous.

Democracy everywhere has emerged when individuals give or withhold consent and rulers are confident enough to accept their verdict. Besides western Europe in 1945 (when democracy was not created but restored), there is almost no example of democracy imposed by external force. Russia, with no experience of it, appears to be rejecting it. The concept of consent in countries such as Egypt, Pakistan and Iran is hesitant, but western pressure, soft or hard, aids the reactionaries.

There is one simple way of honouring Britain's pride in its chosen system: prove it works at home better than any other. That means working tirelessly to refresh it. This is not easy, as Miliband should know in his failed bid to regenerate civic democracy. It may seem small beer, but how can he preach reform to others when he cannot achieve the tiniest reform himself?

The west can invite the world to witness the virtues of democracy. It can deploy the soft power of education, exchange, publicity and aid. But a true democrat cannot abandon Voltaire's respect for the autonomy of disagreement, let alone seek to crush it. Britain can shine its beacon abroad but it cannot impose its values on the world. It has tried too often, and has failed. This is not isolationism. It is fact.