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

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....