Last week I said something stupid about John Maynard Keynes.  Asked to comment on Keynes’ famous observation “In the long run we are all dead,” I suggested that Keynes was perhaps indifferent to the long run because he had no children, and that he had no children because he was gay. This was doubly stupid. First, it is obvious that people who do not have children also care about future generations. Second, I had forgotten that Keynes’ wife Lydia miscarried.

I was duly attacked for my remarks and offered an immediate and unqualified apology. But this did not suffice for some critics, who insisted that I was guilty not just of stupidity but also of homophobia. I have no doubt that at least some students were influenced by these allegations. Nobody would want to study with a bigot. I therefore owe it to students—former and prospective—to make it unambiguously clear that I am no such thing.

To be accused of prejudice is one of the occupational hazards of public life nowadays. There are a remarkable number of people who appear to make a living from pouncing on any utterance that can be construed as evidence of bigotry. Only last year, though not for the first time, I found myself being accused of racism for venturing to criticize President Obama. This came as a surprise to my wife, who was born in Somalia.

The charge of homophobia is equally easy to refute. If I really were a “gay-basher”, as some headline writers so crassly suggested, why would I have asked Andrew Sullivan, of all people, to be the godfather of one of my sons, or to give one of the readings at my wedding?

Throughout my career as a historian, I have regularly written and spoken about Keynes, who had one of the most brilliant minds of the twentieth century. That, of course, is the most important thing about him. You may disagree with his argument that, in a depressed economy, the government should borrow and spend money to stimulate aggregate demand. But you cannot ignore it.

Not for one moment did I mean to suggest that Keynesian economics as a body of thought was simply a function of Keynes’ sexuality. But nor can it be true—as some of my critics apparently believe—that his sexuality is totally irrelevant to our historical understanding of the man. My very first book dealt with the German hyperinflation of 1923, a historical calamity in which Keynes played a minor but important role. In that particular context, Keynes’ sexual orientation did have historical significance. The strong attraction he felt for the German banker Carl Melchior undoubtedly played a part in shaping Keynes’ views on the Treaty of Versailles and its aftermath.

The historian, unlike the economist, is concerned with biography as well as with statistics. Keynes’ first biographer, Roy Harrod, drew a veil over Keynes’ complex private life. But the author of the more recent and definitive three-volume life, Robert Skidelsky, felt no such inhibition. Anyone who reads that great work will find the question of Keynes’ homosexuality treated sensitively and intelligently and related, where appropriate, to his work. Keynes’ fellow members of the Bloomsbury Group would have approved, had they lived to read Skidelsky’s book, for they had no doubt at all that sexual orientation had a significance beyond the narrow confines of the bedroom, and that intellectual life and emotional life were intertwined.

As a historian, I have often had to contend with the question of how far to take the Bloomsbury approach.  Keynes is very far from the only homosexual or bisexual I have written about. In The Pity of War, for example, I discussed the case of T.E. Lawrence, whose real or imagined rape by his Turkish captors was central to his experience of World War I. In The House of Rothschild, I identified at least three members of that illustrious financial dynasty as gay. In Empire, I sketched the lives of both repressed and unrepressed homosexuals who played important roles in the Victorian British Empire.

Yet no one who reads these books could seriously accuse me of harboring a prejudice against gay men (or women). It would be as absurd to accuse me of anti-Semitism for alluding to the fact that the Rothschilds or Warburgs were Jews.

In The War of the World, I sought to explain how warped, pseudo-scientific racial and “eugenic” theories provided a justification for some of the most horrific acts of organized violence in all human history. I could not have been more explicit in condemning such theories. You will find a similar condemnation in Civilization: The West and the Rest. Incidentally, one of the heroes of that book is Frederick the Great of Prussia, who was almost certainly gay.

There is still, regrettably, a great deal of prejudice in the world, racial as well as sexual. There are two strategies we may adopt. One is repression—the old Victorian practice of simply not talking about such things. The other is education. In my writing and teaching, I have labored long and hard to expose precisely what was wrong about the theories that condemned homosexuals, Jews and others to discrimination and death. I have also tried to explain what made those theories so lethally appealing.

The War of the World concludes: “We shall avoid another century of conflict only if we understand the forces that caused the last one—the dark forces that conjure up ethnic conflict and imperial rivalry out of economic crisis, and in doing so negate our common humanity.”

I doubt very much that any of my vituperative online critics have made a comparable effort to understand the nature and dire consequences of prejudice. For the self-appointed inquisitors of internet, it is always easier to accuse than seriously to inquire.

In the long run we are all indeed dead, at least as individuals. Perhaps Keynes was lucky to pre-decease the bloggers because, for all his brilliance, was also prone to moments of what we would now call political incorrectness. In his Economic Consequences of the Peace, for example, he wrote: “Unless her great neighbours are prosperous and orderly, Poland is an economic impossibility with no industry but Jew-baiting.” Even at the time, that was an outrageous thing to say about a country that had suffered grave hardships since its partition in the eighteenth century. But does anyone today seriously argue that we should not read Keynes because he was a Polonophobe?

Ironically, Keynes was even more averse to Americans than to Poles. As he told a friend in 1941: “I always regard a visit [to the US] as in the nature of a serious illness to be followed by convalescence.” To his eyes, Washington was dominated by lawyers, all speaking incomprehensible legalese—or, as Keynes put it, “Cherokee”.

Shock, horror: Even the mighty Keynes occasionally said stupid things. Most professors do. And—let's face it—so do most students.

What the self-appointed speech police of the blogosphere forget is that to err occasionally is an integral part of the learning process. And one of the things I learnt from my stupidity last week is that those who seek to demonize error, rather than forgive it, are among the most insidious enemies of academic freedom.

Niall Ferguson is the Laurence A. Tisch Professor of History at Harvard.