Indeed, this book changed my perception of human nature -- some people are un-reformable. Most of them aren't serial killers, they're just dicks who get their rocks off by controlling other people. Think your asshole boss, or a jerk you knew who was always using people.
It's ridiculous to suggest that 1 in 25 people could be a sociopath. Sociopathy is a disorder, a mental illness, a way in which someone can differ from the norm. If it would affect 4% of the population, it would be an essential part of the norm. Instead of labeling these people as 'sociopaths', why not accept that not everyone has the empathic abilities we'd hope for? Why not accept that, in spite the lack of empathic ability, such people can still lead meaningful lives and can care for others? Calling them 'sociopaths' is just another way of dehumanizing those we don't like, so we don't have to face to darker sides of our own humanity.
What I found truly frightening in that book was the section pointing out the downfalls of the results of the Milgram experiment (most of us will do what we are told by an authority figure, even to the point of torturing/killing) with sociopathic behavior by a minority.
You don't know that sociopathy is a mental illness or disorder. That was also explained in the article. For all you know someone who achieves universal enlightenment might become a sociopath because he/she realizes that we all eventually die and nothing that happens in this world matters, or something like that.
In fact I'd say it's simply an effect of a different world view, and the ones getting caught are the dumber/impulsive ones while the smarter ones are the ones we label as "assholes."
You don't know that sociopathy is a mental illness or disorder.
Neither sociopathy nor psychopathy is listed as a diagnosis in the DSM IV or IDC 10 (the current canonical lists of diagnoses for mental health). Both are listed as descriptors to "Dissocial Personality Disorder" in the ICD 10.
You can't have 1 in 25 people being a sociopath. You can have 1 in 25 people being an antisocial asshole.