Every generation has an opportunity to change the world. Right now, college campuses around the country are home to a moral movement that seeks to reverse centuries of historic wrongs.

This movement is led by students forced to live with the legacy of sexism, with the threat, and sometimes the experience, of sexual assault. It is led by students whose lives have been marred by racism and bigotry. It is led by people who want to secure equal rights for gays, lesbians and other historically marginalized groups.

These students are driven by noble impulses to do justice and identify oppression. They want to not only crack down on exploitation and discrimination, but also eradicate the cultural environment that tolerates these things. They want to police social norms so that hurtful comments are no longer tolerated and so that real bigotry is given no tacit support. Of course, at some level, they are right. Callous statements in the mainstream can lead to hostile behavior on the edge. That’s why we don’t tolerate Holocaust denial.

But when you witness how this movement is actually being felt on campus, you can’t help noticing that it sometimes slides into a form of zealotry. If you read the website of the group FIRE, which defends free speech on campus, if you read Kirsten Powers’s book, “The Silencing,” if you read Judith Shulevitz’s essay “In College and Hiding From Scary Ideas” that was published in The Times in Sunday Review on March 22, you come across tales of professors whose lives are ruined because they made innocent remarks; you see speech codes that inhibit free expression; you see reputations unfairly scarred by charges of racism and sexism.