There have been many posts regarding the mental state of the copilot, most of which conclude that he was suffering from some form of mental illness. He may well have previously received treatment for depression or other ailments, but it is not necessary to invoke some form of psychosis to explain his actions.
For as long as people have lived in social groups, certain bounds have been imposed on individual behaviour. Unacceptable behaviour was punished by expulsion from the group or by other penalties designed to enforce compliance. Religious beliefs also led to cohesion with a given society, although also responsible for many conflicts with other groups. It was the fear of the consequences of getting caught that kept people on the straight and narrow.
Modern society, the lack of religious belief and the general breakdown of extended family groups has contributed to an overall lack of control over the actions of individuals. indeed many people believe that they should have the absolute freedom to do as they wish, although generally with the caveat that their actions should not harm others.
In a society where murder and serious crime is mass entertainment on prime time TV is it any wonder that people grow up with a skewed sense of what is acceptable behaviour?
Given the above statements, I would propose that someone who has achieved their life's dream and who is faced with losing everything due to a medical ailment or disiplinary action may well rationalise that a spectacular murder/suicide is a logical course of action to take. We all want to leave our mark on the world, either by having children, gaining fame or renown by good works, or perhaps by performing an act so shocking that it will be remembered. You don't have to be mad to consider crashing a plane full of passengers into a mountain. It is a logical solution to an unhappy situation if you are not constrained by morals and ethics.
Just another symptom of the pressures of modern society and the breakdown of morals and ethics.
Constant monitoring of pilots will not prevent someone who is determined to do harm from crashing a plane but instilling a sense of responsibility and pride in the job just might help a bit in preventing the mental processes that lead to a crash being the most logical solution to an individual's problems.