THE Hansard entry is an old one, but the exchange could have happened yesterday.

In the Commons, Labour's Frank McElhone, Under-Secretary of State for Scotland, is explaining his difficulty in introducing the Scottish Football Association to the concept of common decency. Indignant, the Honourable Thomas "Tam" Galbraith dissents.

This is May 25, 1977. The Scotland football team is due to play Chile in a "friendly" match in June. The venue chosen is the National Stadium in Santiago, the scene less than four years before of mass torture and murder by Augusto Pinochet's troops. The SFA can see no problem in staging a wee game on the grass where three to four thousand people were slaughtered.

The black joke is that the match will be of no competitive consequence. The Soviet Union has meanwhile been bumped from the qualification round of the 1974 World Cup for the crime, according to the infallible rules, of refusing to play against representatives of this Chilean junta. In contrast, the SFA politburo has threatened to discipline any Scottish player who refuses to travel to South America.

Galbraith has no problem with that. Instead, the member for Glasgow Hillhead in a Tory Party that thinks well of Margaret Thatcher's friend Pinochet, asks McElhone: "Would it not be better if politicians stuck to politics and allowed sportsmen to get on with the game?"

We have been hearing that refrain for half a century and more. The tune changes according to the political purposes of the accusers and the accused, but one feature endures. Left to its own devices, the world of sport will ignore "politics" no matter what. In 1977, Scotland played in Chile while the SFA treated public disgust as an impertinence.

That's the sporting way. Hitler's Olympics, apartheid South Africa, totalitarian China: all horrors can be set aside for the sake of what passes for idealism. Formula One racing while democracy protesters are being clubbed in Bahrain? In 2011, sponsors grew restive and the event was cancelled. This year the security police and the excuses were prepared in advance. Once again, sport declared itself exempt from censure, a law unto itself.

Sometimes the arguments are almost seductive. Why shouldn't the nations of the world set aside their differences and come together in the spirit of friendly competition and, with luck, mutual understanding? Why should sports people have to bear the burden of moral choice amid complicated arguments? How are they to be protected against the risk of exploitation by politicians? Besides, what was ever achieved by a gesture?

Answers to that last question depend on mixed evidence. Pinochet's regime would not have collapsed if Scotland had decided to take their ball and go home. Hitler would not have been deterred in 1936 had some people in Brylcreem and funny shorts taken a stand. Then again, there is little doubt that the world's disdain had a profound effect on sports-loving white South Africans. It spoke of their exclusion from the international community in language they understood.

Something of the sort is in the minds of those demanding that Glasgow's Commonwealth Games must make a statement to those countries, too many countries, still practising barbarism towards homosexuals. It was also Stephen Fry's general idea, no doubt, in his call for a boycott of next year's Russian winter Olympics in Sochi. Under Vladimir Putin's regime, oppression has turned into outright persecution. The illusion of friendly fun in the snow strikes the TV presenter, and many others, as an obnoxious deceit.

But why would Putin differ from Pinochet? What effect would Glasgow's example truly have on a Commonwealth country such as Nigeria, where same-sex relationships risk floggings or executions? The gesture of solidarity could seem self-indulgent, a salve for Western consciences, but serve only to harden attitudes in states that see no problem in theocratic medievalism, or exploit Western criticism for domestic political ends.

Besides, we reveal ourselves as a little pathetic, surely, if our best sanction is withdrawal from the luge, or fine, empty words in Glasgow. As The Herald reported last week, there are 41 countries within the Commonwealth's 54-strong membership with laws against homosexuality. If we are serious about human rights, why do we even remain in such a disreputable club?

The boycott invites retaliation: so much is known. Equally, Britain does not enjoy a monopoly of virtue, to say the least. It is worth remembering, for one example, that the Edinburgh Commonwealth Games of 1986 saw 32 of 59 countries fail to turn up in protest against Thatcher's indulgent attitude towards apartheid. On that occasion, Scotland was the guilty nation, even before Robert Maxwell put his grubby fingerprints on the shambles, just for hosting the affair.

There is a problem, meanwhile, with the choice of evils. Should we take a stand against the persecution of lesbian, gay, bisexual and transgender people? Absolutely. Should we have rejected apartheid? The answer is self-evident. So why was there no boycott of Beijing for the sake of Tibet or Chinese dissidents? How about the absolute rulers of Qatar, their disdain for democracy and their contempt for women's rights? Is that emirate any place for the 2022 World Cup?

The game of boycott has no fixed code and no referees. It has to be played with cunning and skill. That doesn't mean it should not be attempted. For better or worse, sport has a peculiar potency in the 21st century. It amounts to a common international language. No-one should be silenced simply because contradictions abound. Quite the reverse.

The big sporting events matter hugely to states, even when all that is at stake is the weird notion of prestige. The value placed on an Olympics or a World Cup can be judged simply by the obscene amounts governments are prepared to spend on playing host to a few weeks of running around. Even the worst regimes thirst for approval. They are wounded when the world's approval is withheld.

But boycotts and the like have a more precise purpose: they penetrate the fog of propaganda and lies for the citizens of pariah nations. When the sports fixtures stopped, the truth could not longer be hidden from white South Africans. Contrary to any claims made by the Pretoria regime, they had no friends and allies in the world.

Perversely, the failure to boycott can have the opposite effect. The fact that the Beijing Olympics passed off with barely a whimper of complaint internationally allowed China's rulers to pretend to their subjects that their rule was legitimate, accepted and admired by audiences everywhere. Boycotts are a way of telling the truth in simple language.

Glasgow cannot shun its own games, but it can speak the truth to its guests. You could say, in fact, that it has an obligation to do so. If part of the purpose of a major international sporting event is to advertise the virtues and values of the host nation, silence about the things that matter ought to be unthinkable.

It might not end persecution for a single gay person. It will not transform attitudes overnight. But the alternative, as the SFA demonstrated in 1977, is a national disgrace. There are no medals for that.