In his end-of-year address to the Curia, Pope Benedict decried modern society's blurring of gender roles. He also urged the defence of heterosexuality - a cause that he likened in importance to preserving the rain forests from destruction.

The Pope was justified in his criticism of “gender theory”, though the target is obscure and represents more an error than a threat. But in depicting homosexual relations as a threat to the natural order of creation, he is wrong. His remarks inflame rather than inform theological reflection on the intractable issues of human sexuality. And the nature and timing of his intervention detract from the reflective character of his Christian witness.

On other issues, the Pope has shown himself commendably willing to reflect critically on the Church's role in history and society. He has marked the forthcoming 400th anniversary of Galileo's confirmation of Copernican astronomy - conclusions that later earned Galileo condemnation by the Roman Inquisition. The Pope has also argued that Martin Luther was a church reformer rather than a heretic. And the Pope has advanced dialogue with Muslim scholars, mending the damage from his apparent criticism in 2006 of Islam as hostile to reason.

Yet on matters of gender and sexuality, the Pope shows reluctance to move beyond superstition and to embrace tolerance. Granted, his premise that there are biological differences between men and women is plainly true. Such differences are evinced, at the most basic level, in the capacity for bearing children and in relative physical strength. Gender theory goes beyond this unremarkable observation. It claims that biological differences are subordinate to social and educational acculturation in explaining the roles of men and women.

In its generalisations and its dismissal of sex differences, this is a dubious thesis. But it is far from the only dogmatic position in the debate. There is, for example, no empirical warrant for the notion - suggested by a recent president of Harvard, no less - that the low representation of women in scientific disciplines reflects innate differences in scientific aptitude. The Pope has rightly noted that there are innate sex differences without committing himself to this type of fashionable but empty reasoning.

It is thus frustrating that the Pope does not likewise accept the finding that homosexual attraction is part of the natural order. The Pope instead follows his predecessors, who have condemned homosexual acts as a violation of natural law, which is immutable. Homosexuals, according to the Catechism of the Catholic Church, are thus called to chastity.

There is no merit to urging a course on homosexual men and women that offends against science, reason and human kindness. To do so with extravagant rhetoric comparing homosexuality to genuine and urgent issues of social concern is unhelpful. Sexual relations are an important matter for ethical reflection. But the Pope might accept that church teaching has been superseded by science as much as by social mores. For as John Stuart Mill observed, a mode of thinking or feeling that is according to nature is usually accepted as a strong argument for its goodness.