Few would challenge the validity of that concern for an institution which is seen by many to be deeply flawed, with an alarming rate of divorce, domestic violence and child abuse. A few bald statistics make the case: marriages, at 279,000 a year, have reached an all-time low; divorces are now running at 154,000 a year.
More than one in three births now take place outside marriage. Religious weddings - only 42 per cent of all marriages - fell by 10 per cent in 1996. Church of England baptisms have fallen by almost 60 per cent in less than 50 years.
But marriage is a legal as well as a social and religious institution. Reform of that institution will involve legal reforms in a whole range of areas of law - taxation, social security, pensions and immigration as well as family and criminal law.
Surely, then, we are entitled to a higher quality of debate than that to which we are currently subject? Common to so many of those who speak on behalf of "the party of the family" in support of "traditional family values" is the implicit assumption that the only valid family unit is the nuclear one of mother and father and 2.4 children.
Not many would deny that providing a stable background for bringing up children is an important aspect of family life. Certainly it must never be underestimated. But to imply - as many do - that procreation is an essential prerequisite for a family and family life must be wrong.
There are many social units where procreation does not, or cannot, take place, but which would all be widely recognised as families: the single parent and children, the elderly parent dependent on a single adult child, a married couple who cannot or do not wish to have children, even perhaps a same-sex couple in a committed relationship. From the outset it is important to recognise that marriage, as an institution, is constantly evolving and changing.
Compare the late Victorian family, which was extended in terms of members but very narrow geographically, with the contemporary family which is extended geographically but narrow in numbers.
It was refreshing to hear one of the Home Secretary's junior ministers, Lord Williams of Mostyn, speaking in the House of Lords last December, articulating in the case for diversity. He said: "We are not in the business of preaching or prescribing. Families in our society vary infinitely. We live in a diverse society. People are entitled to diverse views about the way in which they wish to run their lives. It is not for me or the government to define precisely what is a family unit. The mark of a civilised society is to accommodate diversity in others."
I would commend to political and religious leaders and social commentators the highly erudite minority judgment of Lord Justice Ward in Fitzpatrick v Sterling Housing Association 1997 where he said: "I would not define a familial nexus in terms of its structure or components. I would rather focus on familial functions. The question is more what a family does than what a family is. A family unit is a social unit which functions through linking its members closely together. The functions may be procreative, sexual, sociable, economic, emotional. The list is not exhaustive. Not all families function in the same way."
If that is a correct analysis then the definition of the family in the late 20th century is much wider than just the traditional or nuclear family.
If the Lord Justice is right, we need to ask our political and religious leaders why the family should continue to be defined in exclusive, rather than inclusive, terms.
It is only against an intellectual analysis of this rigour that the debate on the future of the family and of the marriage contract - and the legislative implications - can properly be conducted. Otherwise, that debate will involve much prejudice, even more hot air, and very little light.
Neither secretaries of state nor archbishops should be allowed to get away with tabloid-aimed sound bites. We are entitled to better than that. As in all good debates, let's start by defining our terms, carefully and precisely, and then see where we get to from there.
Martin Bowley QC is a barrister at 36 Bedford Row, London WC1.Reuse content