Hey, did you hear that President Obama purposefully allowed Ebola to enter the United States so America will be more like Africa?

That’s what conservative activist Phyllis Schlafly said earlier this month, after the first Ebola case reached our shores. In the darker corners of the Internet, others suggested that Obama was spreading Ebola to justify the imposition of martial law; still others charged that government health officials had conspired with pharmaceutical companies to foster the disease and then to hawk a vaccine to cure it.

How could anyone believe that our government would plot to harm its own citizens? Because it’s happened before. Over the past century, the American federal government has repeatedly conspired against the people who elect it. And that’s why so many people suspect that the same thing is happening now.

From 1932 until 1972, the U.S. Public Health Service denied potentially lifesaving treatment to syphilitic African-American men as part of a study of their disease. And starting in the 1950s, the Central Intelligence Agency secretly tested LSD and other drugs on psychiatric patients. It also hired prostitutes to lure unwitting patrons to CIA safe houses, where the agency slipped LSD into their drinks and observed their reactions.

Meanwhile, the CIA and the Federal Bureau of Investigation illegally wiretapped and harassed thousands of civil rights and antiwar activists, including Martin Luther King Jr. The FBI even sent a tape recording of King making love with one of his mistresses to his office, where the package was opened by his wife...