Public reactions to the churches' views on gay marriage currently range from weary indifference to head-scratching bewilderment to angry consternation and all the way to incandescent outrage. Andrew Brown's blogpost attacking two recent church interventions on the question tends towards the third of those responses. It is certainly the case that some such interventions needlessly place the churches in the line of fire.

One of the things attracting Brown's ire was a letter to David Cameron from Anglican Mainstream, an association of conservative Anglicans, responding to the PM's remarks at a reception for lesbian, gay, bisexual and transgender groups at 10 Downing Street. The letter was within its rights to challenge Cameron's ill-informed misrepresentation of the churches' attitudes towards gay people. But it included the unsustainable claim that people of homosexual orientation "have always been fully welcomed" in the churches. Whatever the official teaching of the churches may have been, their practice has all too frequently fallen lamentably and hurtfully short of the goal of "welcome". Many homosexual Christians – including some I have known, and including many who would call themselves theologically conservative – will readily confirm this, at least if asked by someone who by their practice and tone of voice has earned their trust.

But whatever the shortcomings of individual statements on the question, the churches' opposition to gay marriage is now facing the undiscriminating charge that it is driven by "homophobia". In fact, most of their public statements on the matter are only attempts to re-articulate what has long been the most fundamental and enduring principle of Christian (and Jewish) sexual ethics, which is that human beings have been created in such a way that sexual union is appropriately enjoyed in the context of permanent heterosexual commitment. This principle is as much a restraint on heterosexual behaviour as it is on homosexual behaviour (although the churches' voice on the latter would have been a good deal more compelling had they demonstrated a more consistent track record on the former).

The principle is, of course, profoundly disagreeable and sometimes reprehensible to much secular, and some revisionist Christian, opinion. But a position that has shaped one of the most formative ethical practices of western culture cannot be presumptively dismissed as driven by mere prejudice. That is an evasion of reasoned debate.

What is more, most churches are very familiar with the distinction between what they believe about the appropriateness of same-sex sexual relationships and what they believe about how the state should, pursuant to the public good, order those or any other kinds of personal relationships. They are needing to dust down that distinction today. Churches have over the centuries lived, comfortably or contentiously, with a wide variety of legal marriage regimes. Most of them long ago came to terms with the state's permitting remarriage (and many eventually came to allow it within their own ranks). Half a century ago, the Church of England was itself in the forefront of calling for the decriminalisation of homosexual acts. Most have now adjusted themselves, albeit reluctantly in some cases, to the existence of civil partnerships. The question of whether there should be yet another significant change in marriage law – albeit possibly the most far-reaching they have yet had to contemplate – is a challenge that should not be foreign to them.

As they reflect on that question, they will be aware that the last 10 years has seen a rapid collapse in support for the current legal definition of marriage, and examining how they should position themselves in such a radically reconfigured cultural landscape. Most would still prefer to retain the current definition, and some are campaigning vigorously to that end. There have indeed been cogent defences of such a position (here and here) although they have yet to be projected successfully into British public debate.

Yet a growing number are also ready to acknowledge that, in a rapidly secularising as well as deeply plural society, such an option may no longer be democratically sustainable and that new legal models may need to be entertained. One option is at least to call for a separation of civil marriage ceremonies from religious ones, allowing both state and church greater freedom to order their own affairs as they see fit. Another is for civil partnerships to be opened to heterosexual partners, allowing Christians (and others) to consider that legal option for themselves instead of an expanded definition of "marriage" they cannot own. A more radical option would be a universal regime of civil partnerships (open to both heterosexual and homosexual couples, and possibly other household relationships) in which "marriage" is withdrawn from the state's purview, yet with the state remaining fully responsible for the protection of the interests of children or separating partners.

These are not exhaustive, and none has yet won, or is likely soon to win, anything like a consensus. The churches still have a lot of hard work to do to articulate a public position on marriage that is not only true to their own convictions but also credible as a thoughtful contribution to public policy – but then so does David Cameron.