NARA, Japan — In Canada recently, I ran across one of the most anguished mea culpas I’ve encountered in a long time, in a piece prominently displayed in The Toronto Star. Its author, JP Larocque, confessed that in 2008, he foolishly dressed up for Halloween as someone from south of the American border, thus being guilty, all at once, unusually for his considerate homeland, of racial insensitivity, cultural appropriation and a joke in inexcusable taste. That a photo of himself wearing a sign that said, “MEXI-CAN’T” might surface at any moment meant, even more profoundly, that he had “lived with regret ever since.”

I read the piece with care and sympathy, not least because Canada is such a model of global awareness and forward thinking. And it was hard not to feel for this gay man of biracial origin who remained haunted by his tone-deaf cruelty. But a lesser part of me couldn’t help wondering if he hadn’t committed even more egregious sins over the past 11 years (or even 11 days). I certainly have. And whether he didn’t feel that cultural mores and assumptions are always shifting, rendering what was not so exceptional in one era abhorrent in the next. Aren’t all of us at least a little more mature and discerning now than we were a decade ago, partly because we’ve been schooled by our mistakes? Before long, I was beginning to wonder whether Larocque, a writer for the TV series “Slasher,” wasn’t simply replacing ethnocentricity, noxious and unacceptable as it is, with chronocentrism — a term coined in 1974 to suggest among other things, prejudice against other times, rather than against other races.

One of the blessings of the past few years is that many of us have learned to look with more understanding and clarity at the Other. To be different is not to be worse. Yes, a vicious new xenophobia is arising in many parts of the world in response to the erosion of borders, but in part that’s because more and more others are working to look past the stereotypes and dismissive tags of yesterday. Even as many strive so hard to cultivate tolerance when it comes to race, religion and gender, however, those same people seem ever more ready to countenance intolerance when it comes to earlier times — on the grounds that they were intolerant. The shaky assumption behind such chronocentrism is that we have advanced beyond our forebears to a state of relative enlightenment.

In certain respects — the treatment of women, say, and the L.G.B.T.Q. community, as well as of what Canadians call “visible minorities” — we have. Growing up dark-skinned in an England of “Paki-bashing” and the influential demagogue Enoch Powell predicting rivers “foaming with much blood” if people who looked like me continued to be born in his gray-skied land, I’m delighted to return to a newly open and creative London where the average person was born in another country. My four grandparents, all born in India, came of age in a richly multicultured society, but one in which they had little chance of encountering neighbors from Cambodia or Haiti or Ethiopia, as so many New Yorkers or Angelenos can today. Even 20 years ago, I could never have imagined that in 2008 the United States would elect a president who is a living refutation of black-and-white distinctions.