How do I dislike President George Bush? Let me count the ways. Most of them have to do with his contented assumption that 'faith' is, in and of itself, a virtue. This self-satisfied mentality helps explain almost everything, from the smug expression on his face to the way in which, as governor of Texas, he signed all those death warrants without losing a second's composure.

It explains the way in which he embraced ex-KGB goon Vladimir Putin, citing as the basis of a beautiful relationship the fact that Putin was wearing a crucifix. (Has Putin been seen wearing that crucifix before or since? Did his advisers tell him that the President of the United States was that easy a pushover?)

It also explains the unforgivable intervention that Bush made into the private life of the Schiavo family: leaving his Texas ranch to try and keep 'alive' a woman whose autopsy showed that her brain had melted to below flatline a long time before. Here is a man who believes the 'jury' is still 'out' on whether we evolved as a species, who regards stem cell research as something profane, who affects the odd belief that Islam is 'a religion of peace'.

However that may be, I always agreed with him on one secular question, that the regime of Saddam Hussein was long overdue for removal. I know some critics of the Iraq intervention attribute this policy, too, to religious motives (ranging from messianic, born-again Christian piety to the activity of a surreptitious Jewish/Zionist cabal: take your pick).

In this real-world argument, there is a very strong temptation for opponents of the war to invoke the lessons of Vietnam. I must have written thousands of words attempting to show that there is absolutely no analogy between the two conflicts.

Then, addressing the convention of the Veterans of Foreign Wars last week, the President came thundering down the pike to announce that a defeat in Iraq would be - guess what? - another Vietnam. As my hand smacks my brow, and as I ask myself not for the first time if Mr Bush suffers from some sort of political death wish, I quickly restate the reasons why he is wrong to join with his most venomous and ignorant critics in making this case.

1) The Vietminh, later the Vietnamese NLF, were allies of the United States and Britain against the Axis during the Second World War. The Iraqi Baath party was on the other side.

2) Ho Chi Minh quoted Thomas Jefferson in proclaiming Vietnam's own declaration of independence, a note that has hardly been struck in Baathist or jihadist propaganda.

3) Vietnam was resisting French colonialism and had defeated it by 1954 at Dien Bien Phu; the real 'war' was therefore over before the US even landed troops in the country.

4) The subsequent conflict was fought to preserve an imposed partition of a country striving to reunify itself; if anything, the Iraqi case is the reverse.

5) The Vietnamese leadership appealed to the UN: the Saddamists and their jihadist allies murdered the first UN envoy to arrive in Iraq, saying that he was fit only for death because he had assisted in securing the independence of East Timor from Indonesia.

6) Vietnam never threatened any other country; Iraq under Saddam invaded two of its neighbours and declared one of them (Kuwait) to be part of Iraq itself.

7) Vietnam was a victim of chemical and ecological warfare; Iraq was the perpetrator of such illegal methods and sought to develop even worse nuclear and biological ones.

8) Vietnam neither sponsored nor encouraged terrorist tactics beyond its borders; Iraq under Saddam was a haven for Abu Nidal and other random killers and its 'insurgents' now proclaim war on Hindus, Jews, unbelievers and the wrong sort of Muslim.

9) There has for years been a 'people's war' fought by genuine guerrillas in Iraq; it is the war of liberation conducted by Kurdish fighters against genocide and dictatorship. Inconveniently for all analogies, these fighters are ranged on the side of the US and Britain.

10) The Iraqi Communist party and the Iraqi labour movement advocated the overthrow of Saddam (if not necessarily by Bush), a rather conspicuous difference from the situation in Indochina. These forces still form a part of the tenuous civil society that is fighting to defend itself against the parties of God.

11) The American-sponsored regimes in Vietnam tended, among other things, to be strongly identified with one confessional minority (Catholic) to the exclusion of secular, nationalist and Buddhist forces. The elected government in Iraq may have a sectarian hue, but at least it draws upon hitherto repressed majority populations - Kurds and Shias - and at least the American embassy works as a solvent upon religious and ethnic divisions rather than an inciter of them.

12) President Eisenhower admitted that if there had ever been a fair election in Vietnam, it would have been won by Ho Chi Minh; the Baath party's successors refused to participate in the Iraqi elections and their jihadist allies declared that democracy was an alien concept and threatened all voters with murder.

13) The Americans in Vietnam employed methods ('search and destroy'; 'body count') and weapons (napalm, Agent Orange) that targeted civilians. Today, those who make indiscriminate war on the innocent show their hand on the streets of Baghdad and are often the proxies of neighbouring dictatorships or of international gangster organisations.

The above list is by no means exhaustive, but will do, I think, as a caution against any glib invocation of historical comparisons. One might add that among the results of the Vietnamese revolution was an admittedly crude form of market socialism, none the less wedded to ideas of modernisation; a strong resistance to Chinese expansionism (one excuse for Washington's invasion); and a military expedition to depose the genocidal Khmer Rouge regime in Cambodia.

I cannot see how any self-respecting Republican can look at this record without wincing and moaning with shame or how any former friend of the Vietnamese can equate them with either a fascist dictatorship or a nihilistic Islamist death-squad campaign. And now Bush has joined forces with anti-war activist Cindy Sheehan in making the two struggles morally equivalent.

It is true that the collapse of the doomed American adventure in Indochina was followed by massive repression and reprisal, especially in Cambodia, and by the exile of huge numbers of talented Vietnamese. But even this grim total was small compared to the huge losses exacted by the war itself. In Iraq, the genocide, repression, aggression and cultural obliteration preceded the coalition's intervention and had been condemned by a small but impressive library of UN resolutions. Thus, the argument from 'bloodbath', either past or future, has to be completely detached from any consideration of the Vietnamese example.

Bush made his speech just as French Foreign Minister Bernard Kouchner, a distinguished socialist and humanitarian, visited Baghdad and embraced some Iraqi and Kurdish freedom fighters, such as President Jalal Talabani, the leader of a party that is a member of the Socialist International. It takes a special kind of political and moral idiocy to choose such a moment to wax nostalgic for America's inheritance of a moribund French colonialism in Indochina. If one question is rightly settled in the American and, indeed, the international memory, it is that the Vietnam War was at best a titanic blunder and at worst a campaign of atrocity and aggression.

But not all the ironies are at Bush's expense. Change only the name of the analogous country and it becomes fairly clear that in Iraq we are fighting not the Vietcong, but the Khmer Rouge, as the Vietcong eventually had to do on our behalf. The logic of history is pitiless and Bush is not the only one who will find this out.

· Christopher Hitchens is a columnist for Vanity Fair and the author of God Is Not Great