Just recently I read The Intolerance of Tolerance, by D. A. Carson. Carson is one of the best New Testament scholars around, but what he writes in this book (although written from a Christian perspective) has more to do with contemporary politics. His main point is that the concept of tolerance evolved over time to become something impossible to work with.
Being a New Testament scholar, Carson knows very well how language works, and especially how vocabulary accommodates different concepts over time. Not long ago, tolerance was meant to be a secondary virtue. We tolerate things that we don’t like, but that at the same time we don’t believe we should destroy. That was the case between different Protestant denominations early in American history: Baptists, Presbyterians, and so on decided to “agree to disagree,” even though they didn’t agree with one another completely. “I don’t agree with what you are saying, but I don’t think I have to shut you up. I’ll let you say and do the things I don’t like.” Eventually, the boundaries of tolerance were expanded to include Catholics, Jews, and all kinds of people and behaviors that we don’t agree with, but that we decide to tolerate.
The problem with tolerance today is that people want to make it a central value. You have to be tolerant. Period. But is that possible? Should we be tolerant of pedophilia? Murder? Genocide? Can the contemporary tolerant be tolerant of those who are not tolerant?
Postmodernism really made a mess. Postmodernism is very good as a necessary critic to the extremes of rationalism present in modernity. But in and by itself it only leads to nonsense. Once you don’t have anything firm to stand on, anything goes. Everything is relative. Except that everything is relative, that’s absolute. Tolerance today goes the same way: I will not tolerate the fact that you are not tolerant.