All but a few of those theories are found wanting, but some survive and flourish over time, and those comprise our knowledge

A muscular defense of freedom of speech, variance in behaviors and a call for tolerance - The Case for Hate Speech: How Anita Bryant, Jerry Falwell, and Orson Scott Card have advanced the cause of gay rights by Jonathan Rauch.

A generation ago, the main obstacle to gay equality was not hatred, though of course there was a good deal of that. Most people who supported the repressive status quo meant well. The bigger problem, rather, was that people had wrong ideas about homosexuality: factual misapprehensions and moral misjudgments born of ignorance, superstition, taboo, disgust. If people think you are a threat to their children or their family, they are going to fear and hate you. Gays’ most urgent need was epistemological, not political. We had to replace bad ideas with good ones.

Our great blessing was to live in a society that understands where knowledge comes from: not from political authority or personal revelation, but from a public process of open-ended debate and discussion, in which every day millions of people venture and test billions of hypotheses. All but a few of those theories are found wanting, but some survive and flourish over time, and those comprise our knowledge.

The regrettable reality is that truth is not an instantaneous converter. Truth is insufficient on its own to change minds and behaviors. Sustained truth over time is more like it but that means that there is always a frustration to be endured between the time a truth becomes known and the acceptance of that truth. Hence the ubiquitous desire to accelerate things a bit by using some power of coercion. But I think Rauch is right, tempting as it might be to legislate away or boycott opinions you dislike, better to let truth take its own course. Every suppression lends credence to the idea that that being suppressed must be valuable in some way.

The restless process of trial and error does not allow human knowledge to be complete or perfect, but it does allow for steady improvement. If a society is open to robust critical debate, you can look at a tape of its moral and intellectual development over time and know which way it is running: usually toward less social violence, more social participation, and a wider circle of dignity and toleration. And if you see a society that is stuck and not making that kind of progress, you can guess that its intellectual system is not very liberal.

The critical factor in the elimination of error is not individuals’ commitment to the truth as they see it (if anything, most people are too confident they’re right); it is society’s commitment to the protection of criticism, however misguided, upsetting, or ungodly. America’s transformation on gay rights over the past few years is a triumph of the open society. Not long ago, gays were pariahs. We had no real political power, only the force of our arguments. But in a society where free exchange is the rule, that was enough. We had the coercive power of truth.

History shows that the more open the intellectual environment, the better minorities will do. We learn empirically that women are as intelligent and capable as men; this knowledge strengthens the moral claims of gender equality. We learn from social experience that laws permitting religious pluralism make societies more governable; this knowledge strengthens the moral claims of religious liberty. We learn from critical argument that the notion that some races are fit to be enslaved by others is impossible to defend without recourse to hypocrisy and mendacity; this knowledge strengthens the moral claims of inherent human dignity. To make social learning possible, we need to criticize our adversaries, of course. But no less do we need them to criticize us.