I invite all fellow admirers of a tolerant, dynamic, vibrant, liberal, varied and growing world of ideas, expressions, and ways of being to consider, for a moment, that there may indeed have been some wisdom in that famous epigram said to sum up the spirit of Voltaire (though never, apparently, written by him in such words): "I disagree with what this man has said, but I defend to the death his right to say it."
As ugly and embracing of intolerance as such an epigram may seem in practice, perhaps there are reasons, reasons vital to the flourishing of an interesting, varied, free world of expression, that those summing up the spirit of Enlightenment tolerance did not choose to express the appropriate attitude toward things said with which he disagreed—even strongly and passionately disagreed—like this: "I disagree with what this man has said, and I consider him evil for saying it; furthermore, I consider him having said it the most significant thing about him, and that it overshadows any other accomplishment or statement he has ever made. I fervently wish to have him driven from polite society, and consider that anyone who does not enthusiastically join me in so driving him to themselves be evil, or at least incredibly idiotic and not to be trusted—but don't worry, I don't think he should be arrested for saying it."
It may be that the more famous saying indeed embodies the spirit of a lovable, valuable, rich world of discourse; and that the second one perhaps embodies a less open, free, and dynamic, and thus less valuable and interesting, world of discourse.
Also worth considering might be that libertarians in America have had, for reasons that might be somewhat understandable on reflection, to cultivate (perhaps to a fault) that original Voltairian spirit, as unpopular as it is in America. Among libertarians' intellectual background is the likes of Nock, who believed that it wasn't enough for a judge to refuse to convict girls for walking naked down the street; that true liberal freedom meant no one even noticed. Also, of course, in libertarians' intellectual background is Mises, who wrote that "Liberalism…must be intolerant of every kind of intolerance," but that statement might be seen to have a strange loop in it.
Libertarians have a set of peculiar beliefs about the proper use of force, generally based in a moral vision as well as a vision of human wealth, happiness, and flourishing. They consider their ideas of liberty and free markets salubrious, even glorious. They also find that almost everyone around them—generally including dearly beloved friends and family—hews to an alternate set of beliefs about what is proper and how to treat other human beings, beliefs utterly opposed to theirs in important respects. Indeed, the very common view that it is proper to use violent force against nonaggressors is one that the libertarian could fairly, from their perspective, consider evil.
And yet, somehow it rarely seems proper to the libertarian to hew with grim consistency to some of the conclusions about how to behave in the social world that might follow from that. They have never managed, for the most part, to be sternly and angrily opposed in high moral dudgeon to most of the people around them.
Indeed, looking at those who have chosen that path, they see models that seem inappropriate There seems something worth mocking and rejecting in the traditional Objectivist's sense of a duty to practice harsh lordly disdain and refusal to truck with those who reject reason and liberty for irrationality and evil. Neither does it seem prudent or lovely to most libertarians to emulate the driven-to-his-compound-with-guns style of the man who decides to finally and firmly remove himself from the statist world's endless evils of theft and oppression, back to the wall, prepared to fight if need be to show how he refuses to give any sanction to evil ideas—and evil practices.
For reasons perhaps difficult to articulate in a raw moral calculus, such ways of dealing with ideas—and practices!—that harm innocents by the millions seem even to most libertarians unlovely and impractical. It would lead to a social world, as long as they have failed to educate the rest of the world around them in libertarian principles, too ugly and divisive to warmly embrace. Such a hardline approach of complete moral disavowal and disengagement from people who advocate bad ideas is generally eschewed, even when those ideological differences aren't merely about words or thoughts, but actuate in what the libertarian sees as actual theft, assault, tyranny, and murder on a daily basis.
This might shed some light one why many American libertarians tend toward such serious and dedicated classical Voltairianism, even when the rest of the world thinks them foolish, misguided, or evil to think, and behave, in that overly tolerant manner.