There have always been people who think that evil is more effective than good, and who want to dispense with ethical behavior in the name of "practicality". The 9/11 attacks were a god-send to these people, because it gave them the perfect excuse to pursue their evil agenda. "The terrorists are the worst enemy America has ever faced," they claimed. "The terrorists are pure evil, and the only way we can fight back is by being evil ourselves." It helped that one of the most evil politicians in the country, Dick Cheney, was basically running the government.
So it was that the American government embraced the cult of evil: torture, and aggressive warfare, and the deliberate targeting of innocent victims. 24 gave the cult of evil a prominent place in popular culture, and introduced a new American "hero": Jack Bauer, the man who is always ready to torture a suspect, and who is always right to resort to torture.
The cult of evil has also spread to economic policy. Our political commentariat has nothing but praise for politicians who make the "hard choices" to make ordinary people suffer so that the wealthy can become even more wealthy. The willingness to inflict unnecessary pain on the helpless has become the cardinal political virtue of our times.
And now we've reached the point where the crowd at a Republican candidates debate not only cheers Rick Perry for exectuting hundreds of people, they cheered him for executing an innocent man, because "it takes balls to execute an innocent man".
So, welcome to the post-9/11 America: a land in thrall to the cult of evil.