In this season of goodwill, I have been trying to think of a kinder adjective to describe "of or pertaining to the revelation of the angel Moroni". Moronish? Moronical? The angel Moroni allegedly appeared in the 1820s to a young American treasure hunter called Joseph Smith, and led him to some golden plates buried on a hillside near his home in western New York. Allegedly written in an otherwise unknown language called Reformed Egyptian, and deciphered with the aid of two stones called Urim and Thummim, these texts became the Book of Mormon, regarded by Mormons as divine revelation alongside the Bible. "Mormon", Smith explained in a letter to a newspaper, derives from the Reformed Egyptian word mon, meaning good, "hence with the addition of more, or the contraction mor, we have the word Mormon; which means, literally, more good".

In this holy book, North America was described as "a land which is choice above all other lands" (II Nephi 1:5), and 19th-century Americans were assured, in a kind of retrospective prophecy, that "it shall be a land of liberty" (II Nephi 1:7). What is more, if the Native Americans converted to the true faith, they would have the chance to become again "a white and a delightsome people" (II Nephi 30:6). (The official online version has corrected this to "a pure and a delightsome people".) Adherents of this Church of Jesus Christ of Latter-day Saints can, by their own strenuous efforts and good works, themselves aspire to become gods. Failing that, they can aspire to become the next best thing - president of the United States.

The only reason we are recalling this Moronish wisdom is, of course, that one leading Republican contender for the presidency, Mitt Romney, professes to be a devout Mormon, and his religion has become an election issue. According to a profile in the New York Times, Romney's father, George, was born in Mexico "in a colony of Mormons who had fled a crackdown on polygamy ... As a Mormon missionary, he was assigned to proselytise in London from a soapbox in Hyde Park, where he developed a gift for salesmanship that became the hallmark of his career". Mitt Romney did his own Mormon missionary work in France. Romney's Mormonism is a problem for many evangelical Christians from the religious right, who would otherwise be his natural constituency. Instead, they might prefer the Southern Baptist Mike Huckabee, who merely takes the book of Genesis literally.

To fend off this threat, Romney delivered a speech this month that drew the line in another place, not between Mormons and true Christians but between everyone of faith and the godless rest. Only the former, he implied, can be true Americans: "We should acknowledge the creator as did the founders - in ceremony and word." "You can be certain of this," he attempted to reassure US voters, "any believer in religious freedom, any person who has knelt in prayer to the Almighty, has a friend and ally in me ... we do not insist on a single strain of religion - rather, we welcome our nation's symphony of faith."

So it really doesn't matter what irrational belief you have as long as you have some irrational belief. The one thing apparently putting you beyond the pale, disbarring you from full belonging to the national community, is to claim that science-based reason suggests, with a degree of probability verging on certainty, that there is no Almighty. The Romney formula is EBA - Everyone But Atheists.

This will not lose him many Republican votes, but as a recipe for a free country it's unacceptable. At the very least, religious politicians in free countries must find a language that gives equal footing in the public square to those of all faiths and those of none. Even in Britain we encounter these attempts to suggest that "faith" is somehow intrinsically superior to a lack of religious belief. Just before Christmas the former home secretary Charles Clarke emailed me the text of a lecture he had delivered on this subject. Clarke's lead proposition was that "first and foremost, faith is generally a force for good".

Whether as a historical or contemporary statement, this does not hold up. Since for most of history most men and women have had some faith, and even in the modern world most still do, almost everything done by humans to humans, or to the natural world, has been justified by one faith or another: a lot of very good things; and a lot of very bad things. It's as ahistorical to deny that people have done what we secular liberals would consider to be good out of what they believed to be religious motivation, as it is to deny that people have done terrible things out of what they believed to be religious motivation.

My position on this is empirical: by their fruits ye shall know them. Maybe one day everyone will become convinced of the scientific truths of Darwinism, although science itself is throwing up evidence suggesting some sort of religious instinct is, so to speak, hard-wired. The battle of ideas over what is ultimately true must continue to be fought. In the meantime, it matters less what our politicians believe in that religious corner of their minds and more what they do. If they consistently come up with the right policies, while believing themselves to be a Mormon, a Catholic or a Muslim, we should support them. If they come up with the wrong policies, despite being a scientific atheist, we should oppose them.

My residual problem with Romney being a Mormon is not that Mormonism is a faith (the atheist's problem), or that Mormonism is not unambiguously Christian (the Christian's problem), but that it seems such a wacky collection of man-made Moronical codswallop. And I do find myself wondering - even if he is a natural conservative, even if Mormonism is, as he puts it, "the faith of my fathers", including the most recent father whom he hero-worshipped - how on earth a well-educated man who aspires to lead the most powerful and modern nation in the world can seriously believe this stuff. Ah well, there's nowt so queer as folk.

timothygartonash.com