Elizabeth Powers explains for Commentary magazine readers how some left-of-center thinkers approach political debates with false premises.

What we consider “good,” “best,” “excellent,” and so on are matters of what, since the 18th century, has been called taste. And if there is one thing we can all agree on, it’s that taste is an individual thing: I like Manet, you like Lucian Freud. Our personal preferences, for this is what they are, will probably change over our lifetime. By the time we reach middle age, what impressed us when we were 20 will seem immature instead. We “grow”: We read more books, we see more movies. Our opinions evolve.

Nevertheless, when we use words such as excellent, we feel that what we love will also be loved by everyone else, especially our kind of people: our spouse, our friends, our colleagues. We attribute our own feelings to others. To a great extent, this desire to share with others what we love is a very human thing: It indicates a certain universality. At the same time, our judgments of taste—for instance, that a painting or a book is excellent or not even worth considering—are value judgments, and they have a coercive aspect. When I assert that something is good, it does not mean that you too might find it good; it means that what I love, you too should love. This would not be a problem if the matter were restricted to books, movies, art, or, increasingly, food—subjects on which few of us come to blows.

But such value judgments encompass the social and political realms as well, with destructive, cascading effects. We can call it “the liberal fallacy.”

For liberals, the correctness of their opinions—on universal health care, on Sarah Palin, on gay marriage—is self-evident. Anyone who has tried to argue the merits of such issues with liberals will surely recognize this attitude. Liberals are pleased with themselves for thinking the way they do. In their view, the way they think is the way all right-thinking people should think. Thus, “the liberal fallacy”: Liberals imagine that everyone should share their opinions, and if others do not, there is something wrong with them. On matters of books and movies, they may give an inch, but if people have contrary opinions on political and social matters, it follows that the fault is with the others.

Of course, true liberals avoid this fallacy. They believe in free expression and the competition of ideas.