Not simply insane

According to a press release by Royal College of Psychiatrists, terrorists are not technically insane.

The term 'terrorist' is not a psychiatric diagnosis, the Royal College of Psychiatrists heard today. Dr Andrew Silke, a forensic psychologist at the University of Leicester and an adviser to the UN, said the outstanding characteristic of terrorists is 'normality' with forensic assessments of terrorists from the Baader Meinhof to Al Queda revealing high levels of mental health.
The widespread view that terrorists are isolated, vulnerable young men with paranoid or borderline personality disorders, is false. It is entirely perpetuated by experts relying on second hand reports, he told the conference.
A survey of 180 members of Al Queda revealed that all came from middle or upper class backgrounds, with two thirds being college educated, one in ten with a postgraduate degree and 73 per cent married with children, he said.
Dr Wilfred Rusch, a Berlin psychiatrist employed by the German Government to assess Baader Meinhof terrorists concluded that none of these people are crazy - there is no psychiatric explanation as to why they were involved in terrorism.

This makes intuitive sense when one considers that those who are unable to maintain the appearance of normality are unsuitable for use as sleepers. Therefore, those with impulse control are selected for. So what does drive them?

Dr Silke said it was important to understand that the word terrorist is a political not a psychiatric diagnosis, with catalyst events, usually involving violence, creating the energy and the desire for revenge and the wish to punish the state.

More recently, brain scans revealed portions of the brain which are hardwired to enjoy anticipating revenge. It's a key piece of the puzzle.

Planning revenge sparks enough satisfaction to motivate getting even — and the amount of satisfaction actually predicts who will go to greater lengths to do so, report Swiss researchers who monitored people's brain activity during an elaborate game of double-cross...
But beyond helping to unravel how the brain makes social and moral decisions, the study illustrates growing interest in the interaction between emotion and cognition — which in turn influences other fields such as how to better model the economy.
The new study chips "yet another sliver from the rational model of economic man," said Stanford University psychologist Brian Knutson, who reviewed the Swiss research. "Instead of cold, calculated reason, it is passion that may plant the seeds of revenge," he said.
People often are eager to punish wrongdoers even if the revenge brings them no personal gain or actually costs them something. From a practical standpoint, that may seem irrational.

Apparently irrational, but seemingly normal, and certainly rational so far as they can plan and achieve operational goals. Regarding hearts and minds, the former is far more volatile.