Last week, I wrote a column on “paranoid libertarians,” defined as people who have a wildly exaggerated sense of risks to liberty, who adopt a presumption of bad faith on the part of government, who have a sense of victimization, who ignore the problem of tradeoffs, and who love slippery-slope arguments. Paranoid libertarianism can be found on both the right and the left, and as I noted, paranoid libertarianism should be distinguished from libertarianism as such.

In some circles, the column has produced a bit of stir and a cry of “foul.” Invoking Justice Elena Kagan’s skeptical questions during oral argument in the Defense of Marriage case, Damon Root at Reason responded, “Is Elena Kagan a ‘paranoid libertarian’? Judging by Sunstein’s definition, the answer is yes. Welcome to the brave new world.” A commentator at Antiwar.com asked, “Is it really necessary to catalogue the long history of US government surveillance and targeting of dissident political groups?”

It is true that many people distrust government, and they fear that it will overreach. Are they paranoid?

To a significant extent, our constitutional system is built on such distrust. Consider James Madison’s words: “If angels were to govern men, neither external nor internal controls on government would be necessary. In framing a government which is to be administered by men over men, the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself.”

Nor is our constitutional tradition indifferent to the risk of slippery slopes. In protecting freedom of speech, both judges and ordinary citizens like to say: “We can’t allow the government to regulate this form of speech (say, Nazis marching in Skokie, Illinois), because once we do, we’ll have trouble drawing the line.” If we are concerned about liberty, we can’t scoff at those who fear the slippery slope.

It should not be necessary to say that those who insist on safeguards for freedom, and who are unwilling to trust public officials, have learned history’s lessons, and are anything but paranoid. And libertarians, who believe in a robust system of private rights, are speaking on behalf of an important strand in America’s political culture.

Nonetheless, it remains true that there are genuinely paranoid forms of libertarianism, reflecting wildly exaggerated, and evidence-free, judgments about the supposedly grave risks of even modest initiatives (involving, say, gun control, religious ceremonies at public universities, and environmental regulation). Of course political paranoia (speaking colloquially, not clinically) comes in many varieties.

As Richard Hoftstadter shows in his great essay "The Paranoid Style in American Politics," McCarthyism was a distinctive form of political paranoia, and it was anything but libertarian. Other varieties target corporate power, particular religions, and political movements of diverse kinds.

In American politics, no group has a monopoly on the paranoid style, but very few of them are entirely immune from it.

(Cass R. Sunstein, the Robert Walmsley University professor at Harvard Law School, is a Bloomberg View columnist. He is a former administrator of the White House Office of Information and Regulatory Affairs, the co-author of “Nudge” and author of “Conspiracy Theories and Other Dangerous Ideas,” forthcoming in March.)

To contact the writer of this article: Cass R. Sunstein at csunstei@law.harvard.edu.

To contact the editor responsible for this article: Tobin Harshaw at tharshaw@bloomberg.net.