It's considered a law almost as fixed as gravity that the way the country is governed interests only those who have hair dye in their bathroom cabinets or are tootling around on brand-new knees.

The young, we are constantly told, have no interest in politics.

So we should be cheered, I suppose, by the fact that a highly political outfit, Scotland For Marriage, has just recruited its 50,000th supporter, who happens to be a 20-year-old student. According to this group, who claim this number marks only the start of their ambitious nationwide recruitment drive, their membership already outstrips that of paid-up members to all Scotland's political parties combined.

Before you reach for a hanky, thinking that this is a romantic body keen to gather as many lovers into their fold as possible, let me stop you there. Scotland For Marriage would be more accurately named Scotia For Olde Worlde Marriage.

Odd, isn't it, that while party politics is losing its lustre, and not just for the youthful, a non-politically affiliated group of petitioners dedicated to upholding traditional marriage is proving a runaway success with all ages. Their newest signatory summarised the beliefs of Scotland For Marriage as concisely as if the tenets were tattooed on his palm: "Marriage is between one man and one woman to the exclusion of others with a view to the procreation of children."

Put aside, for the moment, the thorny issue of a man and a woman marrying late, when procreation is not only unlikely but unwise. They might be as evangelical as Billy Graham, but by Scotland For Marriage's definition this couple already breaches one of the main requirements for a conventional Christian marriage.

This, however, is to tap dance on the head of a theological pin. Far more pressing, and to my mind disturbing, is that so many want to kill the government's impending debate on legalising gay marriage. Whether this comes from religious conviction, fear of change, or a prejudice so deep-rooted it can only be called primitive, is not clear. My guess would be, however, that there is a substantial overlap between the Scotland For Marriage campaigners and religious hardliners.

Fair enough. Those whose evangelical beliefs mean they cannot accept practising homosexuals let alone marriage between them, who claim to love the sinner but hate the sin, are entitled to their views. What alarms me, however, is the zeal with which the campaign is being rolled out across Scotland. Apparently, Scotland For Marriage has a network of activists in every constituency encouraging voters to put pressure on their MSPs not to vote for any change in marital law.

When an organisation goes to such lengths, when personal beliefs become a bandwagon on which thousands of like-minded individuals are invited, or on to which switherers are cajoled, it takes on a sinister tone. Such co-ordination might be well within our democratic laws, but it smacks of intimidation.

So what is it about changing the matrimonial status quo that has galvanised such enthusiastic opponents? I can recall no religious marches of late to protest about poverty or the gap between rich and poor, about global warming, child abuse, disability allowances, or Syria. Yet these, and many others, are issues that devout Christians ought to take as seriously as homosexual marriage, and whose consequences for society as a whole will certainly be far more grave than a few committed gay couples wearing wedding rings and showing marriage is still an institution to be treasured.

Stonewall, the gay rights group, recently conducted a poll that shows homophobia in Britain remains rife. I am not accusing all supporters of Scotland For Marriage of being of that ilk, though no doubt some are. But what a number of Stonewall's respondents found is that attitudes in society often lag far behind legislation.

One needs think only of slavery, or women's rights, or the smoking ban to see that sometimes our leaders must take the initiative, regardless of naysayers and no matter how loudly they shout. In the case of Scotland For Marriage, one hopes MSPs will place these activists' views in a wider context: not of upholding tradition or safeguarding religious shibboleths, but of improving our world for all. Holyrood's ability to do just that is one of the few things I have faith in.