Johann Hari: Here are the real reasons to oppose the Pope

He is one of the primary defenders of priests who tell people condoms cause Aids

Sigmund Freud identified a phenomenon called "the narcissism of small differences". He argued you are more likely to hate somebody who is very, very similar to you than somebody who is drastically different. This week, Freud's principle has been demonstrated with cruelly plodding logic across the world: in the Bavarian lecture where God's Rottweiller finally slipped his leash, in the bullets fired into a nun's back in Somalia, and in a gaggle of jihadis rallying outside Westminster Abbey with banners saying "Execute the Pope".

Joseph Ratzinger and the Islamists calling for his decapitation believe they have direct access to an invisible supernatural being called "God". Both believe this God wills them to make decisions that have led to the horrific deaths of tens of thousands of people. Both believe this God finds secular democratic Europe disgusting, an atheistic bog dominated by a "culture of death". Both hate feminism and gay rights and sexual freedom. Both believe they are infallible, and that the billions who refuse to follow them are incurring the wrath of the Creator of the Universe. The only real difference is the name they give to this creature, and a few added textual tweaks on either side.

The tragedy is that when there are so many good reasons to hate Joseph Ratzinger, this week's rioters have chosen one of the few bogus ones. For more than a decade, he has been one of the primary defenders of priests who go to the poorest, most vulnerable people in the world and tell them condoms are the cause of Aids. In the past year, I have sat in two Catholic churches thousands of miles apart and listened while a Catholic priest told illiterate people with no alternative sources of information that condoms come pre-infected with Aids and are the reason people die of it. In Bukavu, a crater-city in Congo, and in the slums ringing Caracas, Venezuela, people told me they "would not go to Heaven" if they used condoms, and that condoms contain tiny invisible holes through which the virus passes - the advice their priest had doled out.

These churches were not a pair of freakish exceptions. A slew of human rights groups have documented how these lethal lies have been orchestrated by the Vatican itself, with Ratzinger humming along in the background. The president of the Vatican's Pontifical Council for the Family, Cardinal Alfonso Lopez Trujillo, said: "The Aids virus is roughly 450 times smaller than the spermatozoon. The spermatozoon can easily pass through the 'net' that is formed by the condom."

In order to make people more likely to choose abstinence - the only Holy route - these priests are making premarital sex sound deadly as well as sinful. In El Salvador, the Vatican's representatives even successfully helped get a warning on to packs of condoms saying they don't work. Ratzinger has kept these people in place; many have been promoted. There were rumours earlier this year that Ratzinger was poised to say condoms were permissible - within marriage, where one partner is HIV positive. Even if it happens, this overdue flick of sanity would come too late for tens of thousands of innocent people.

But there is a deeper philosophical repugnance to Ratzinger beneath these individual decisions. His recent lecture was devoted to the premise that the free pursuit of reason will lead all people to a rational belief in the Christian God described in the Bible. (You know - the God who explicitly supports slavery, commits genocide against the Amelkites, stones prostitutes, and feeds small children to bears.) The Christian God is Reason Personified, while the Muslim God is "beyond reason" - hence the fuss. But this intra-superstitious squabble is not the real outrage.

However much he swears it is not, this argument is deeply anti-Enlightenment. The central insight of the Enlightenment is that there are two fundamentally different ways to understand the world. One is divine revelation, where a being contacts you from another realm and discloses some truth. (Another word for this is "hallucination".) The second method is reason - observing the world empirically, and drawing conclusions from the things we observe. The ultimate expression of reason is the scientific method. These approaches are fundamentally contrasting, and you cannot simply weld them together with contorted theological trickery.

By claiming that divine revelation leads to reason - indeed, is its central underpinning - Ratzinger is subtly attacking the core principles of the Enlightenment. There is nothing we can observe in the world that leads us rationally to conclude a magical creature created it. But Ratzinger wants to be able to claim the fruits of the Enlightenment, such as science, without following its basic principles. Whenever people do try to stretch reason to accord with faith - as he demands - they invariably produce contorted, corrupted unreason such as the absurdity of "intelligent design theory" (which should be called Creationism 2.0).

Of course, none of Ratzinger's lies justify threats of violence against him. For decades now, he has been saying atheists have "no morality" and are "depraved", and that homosexuality is "an objective disorder" and "evil" - far worse insults than last week's cagey half-slur on Muslims - and it never occurred to us to respond by attacking Catholic nuns working with the starving. We mocked the sex advice of an elderly virgin, gave money to aid agencies trying to correct his poisonous lies, and got on with our lives. The cool balm of reason is the way to put down God's most rabid Rottweiler - not the furious fire of a parallel fundamentalism.

j.hari@independent.co.uk