Recently, the British government published a list of 16 people barred from the country. Eight Muslim clerics, writers and political advocates were among them. And then there was a right-wing radio host from San Francisco, an anti-gay pastor and his like-minded daughter from Kansas, and a former grand wizard of the Ku Klux Klan from Florida.

Their crimes:“spreading hate.”

The first reaction of many was shock. To ban someone for what they say (like the radio host, Michael Savage) rather than what they do? That’s out of place in a democracy, right?

According to Ben Ward of Human Rights Watch in London, the British list was mainly about the Muslims - the American right-wingers were for political balance - and shows just how much Britain and countries like France and Spain still worry about the militant Islamists in their midst.

But of course we shouldn’t be so naive. People are stopped from traveling all the time - around the globe and in the United States. They are held back for minor and major infractions, but also for what they think or say, although Britain more or less stands alone in making public who is banned.

Apart from common misdeeds like heroin addiction and financial fraud, the United States will stop you for suspected terrorist activity - and for this it has a list, although it is not public.

To make the Coordinated Terrorist Watchlist, which has been maintained since 2003, you have to be“reasonably”suspected of“involvement in terrorist activity,”according to Chad Kolton, spokesman for the F.B.I.’s Terrorist Screening Center in northern Virginia.

The list has 400,000 names. About 95 percent of people on the list are not United States citizens, and the vast majority are not in the country. Recently, a Justice Department report found that about 24,000 names had been kept on the list in error because of outdated or irrelevant information.

During the cold war, the United States had a rich tradition of excluding people it didn’t like on ideological grounds. Morton H. Halperin, a consultant to the Open Society Institute in New York, an organization that promotes democracy around the world, said the McCarran-Walter Act of 1952 targeted Communists but in the following decades was applied rather more broadly.

Although Congress eventually repealed the act, the power of“ideological exclusion”persists today in the USA Patriot Act, according to Caroline Fredrickson of the American Civil Liberties Union.

The act allows the authorities to bar foreigners who use a“position of prominence within any country to endorse or espouse terrorist activity.”In a letter in March to Secretary of State Hillary Rodham Clinton, among others, the A.C.L.U. and other human rights groups said that dozens of scholars and intellectuals were being banned from the country“not on the basis of their actions but on the basis of their ideas.”

Lists or no lists,“many governments exclude people whose views they don’t like,”said Aryeh Neier, president of the Open Society Institute.“They simply deny them visas. China excludes people all the time. They don’t ordinarily give explanations.”