I recently finished reading Without Conscience: The Disturbing World of the Psychopaths Among Us by Robert Hare. As the title suggests, psychopaths are qualitatively different from other people, literally having no conscience. The book (and another on the subject, The Sociopath Next Door by Martha Stout) convinced me that this difference really exists. Before that, I assumed that all people who behaved differently from me just had different values or loyalties.
According to Hare, psychopaths have no difficult lying or even contradicting themselves in the same conversation. He gives the following beyond satire examples (pp. 125-127):
When asked if he had ever committed a violent offense, a man serving time for theft answered, "No, but I once had to kill someone."
A woman with a staggering record of fraud, deceit, lies, and broken promises concluded a letter to the parole board with, "I've let a lot of people down....One is only as good as her reputation and name. My word is as good as gold."
A man serving time for armed robbery replied to the testimony of an eyewitness, "He's lying. I wasn't there. I should have blown his fucking head off."
When asked, "Did you actually carry around in your briefcase blank power-of-attorney forms?" his reply was, "No, I didn't carry them around, but I had them in my briefcase, yes."
[Convicted serial killer Elmer Wayne Henley answers an interviewer by saying]: "I'm not a serial killer." The interviewer than says, "You're saying you're not a serial killer now, but you've serially killed." Henley replies, with some exasperation and condescension, "Well, yeah, that's semantics."