AFTER THE devastating disease of polio was finally conquered by vaccines in the 1960s, the number of people afflicted declined almost to the vanishing point. Some people then began to see no need to take the vaccine, since apparently no one was getting polio anymore, so who was there to catch it from?
The result was a needless resurgence of crippling and death from this terrible disease.
The kind of thinking involved in the polio fallacy has appeared in many other contexts. When some public disorder gets under way and a massive arrival of police on the scene brings everything under control immediately, many in the media and in politics deplore such "overreaction" on the part of the police to a minor disturbance.
It never occurs to such people that it was precisely the arrival of huge numbers of cops on the scene that brought the disturbance to a screeching halt without having to use force.
During the Cold War, communist expansionism around the world somehow never struck Western Europe, which was protected by the American nuclear umbrella - and which often accused the United States of unnecessary militarism. American military power was like the polio vaccine that was considered unnecessary.
The latest version of the polio fallacy is the demonizing of the Patriot Act. Some people are yelling louder than ever that they have been silenced, that we have had our freedom destroyed, all as a result of the Patriot Act.
Let us go back to square one, to 9/11, which was the reason for passage of the Patriot Act.
Do you remember how long every major public event - the World Series, Christmas celebrations, the Super Bowl - was a time of fear of a new terrorist attack? Do you remember all the advice to stock up on medicines or food, so that we could ride out any new terrorist onslaught?
Do you remember all the places that terrorists were expected to strike? The different colors of national alerts being announced regularly?
Now, after years have passed without any of these feared disasters actually happening, the eroding of a sense of danger has led many to repeat the polio fallacy and act as if the dangers from which we have been protected did not exist - and that the enhanced protection is therefore unnecessary.
The many crackdowns on domestic terrorists under the Patriot Act, as well as the ability to intercept and disrupt their communications under the powers of that act, receive little or no credit for the fact that there has been no repetition of anything like 9/11.
The man principally responsible for law enforcement crackdowns on terrorists in the United States during this dangerous period - Attorney General John Ashcroft - not only received no gratitude for our safety, but the complacency to which that safety led allowed many to indulge themselves in the luxury of vilifying Mr. Ashcroft at every turn.
Like the police who arrive in large numbers to quell disturbances and are then accused of "overreacting," the Patriot Act has been depicted as an overreaction to terrorist activity. Indeed, the very word "terrorist" has been banned in much of the politically correct media.
The Patriot Act is no closer to perfection than anything else human. It has costs, as every benefit has had costs, hard as it is for many among the intelligentsia to accept anything less than "win-win" situations.
"I have a real problem with fascism," as one woman in a trendy California bookstore said fiercely when discussing the Patriot Act.
She was aghast when I replied, "I hadn't noticed any fascism."
Thomas Sowell is a senior fellow at the Hoover Institution at Stanford University. His syndicated column appears Thursdays in The Sun.