The Canadian immigration minister Jason Kenney gazetted in the Sun yesterday morning that I was to be excluded from his country because of my views on Afghanistan. That's the way the rightwing, last-ditch dead-enders of Bushism in Ottawa conduct their business.

Kenney is quite a card. A quick trawl establishes he's a gay-baiter, gung-ho armchair warrior, with an odd habit of exceeding his immigration brief. Three years ago he attacked the pro-western Lebanese prime minister, Fuad Siniora, for being ungrateful to Canada for its support of Israeli bombardment of his country. Most curiously of all, in 2006 he addressed a rally of the so-called People's Mujahideen of Iran, a Waco-style cult, banned in the European Union as a terrorist organisation. On one level being banned by such a man is like being told to sit up straight by the hunchback of Notre Dame or being lectured on due diligence by Conrad Black. On another, for a Scotsman to be excluded from Canada is like being turned away from the family home.

But what are my views on Afghanistan which the Canadian government does not want its people to hear? I've never been to Afghanistan, nor have I ever met a Taliban, but my first impression into the parliamentary vellum on the subject was more than two decades ago. At the time the fathers of the Taliban were "freedom fighters", paraded at US Republican and British Tory conferences. Who knows, maybe even the Canadian right extolled these god-fearing opponents of communism. I did not, however.

On the eve of their storming of Kabul I told Margaret Thatcher that she "had opened the gates to the barbarians" and that "a long, dark night would now descend upon the people of Afghanistan". With the same conviction, I say to the Canadian and other Nato governments today that your policy is equally a profound mistake. From time to time and with increased regularity it is a crime. Like the bombardment of wedding parties and even funerals or the presiding over a record opium crop, which under our noses finds its way coursing through the veins of young people from Nova Scotia to Newcastle upon Tyne. But it is worse than a crime, as Tallyrand said, it's a blunder.

The Afghans have never succumbed to foreign occupation, heaven knows the British empire tried, tried and failed again. Not even Alexander the Great succeeded, and whoever else he is, minister Kenney is no Alexander the Great. Young Canadian soldiers are dying in significant numbers on Afghanistan's plains. Their families are entitled to know how many of us believe this adventure to be similarly doomed and that genuine support for troops - British, Canadian and other - means bringing them home and changing course.

To ban a five-times elected British MP from addressing public events or keeping appointments with television and radio programmes is a serious matter. Kenney's "spokesman" told the Sun, "Galloway's not coming in ... end of story." Alas for him, it's not. Canada remains a free country governed by law and my friends are even now seeking a judicial review. And there are other ways I can address those Canadians who wish to hear me.

More than half a century ago Paul Robeson, one of the greatest men who ever lived, was forbidden to enter Canada not by Ottawa but by Washington, which had taken away his passport. But he was still able to transfix a vast crowd of Vancouver's mill hands and miners with a 17-minute telephone concert, culminating in a rendition of the Ballad of Joe Hill. Technology has moved on since then. And so from coast to coast, minister Kenney notwithstanding, I will be heard - one way or another.

• George Galloway is Respect MP for Bethnal Green and Bow gallowayg@parliament.uk