Still very early days in this investigation and at this stage we have no idea if the cause will ever finally be established beyond doubt.
One current line of thought is the pilot suicide one. I sincerely hope this does not prove to be the case. We already see some aviation authorities twitching at this likelihood - the DGCA in India is reported as looking at introducing psychometric testing for pilots as a result of MH370 even before the cause is declared (or even known):-
[URL="http://www.business-standard.com/article/companies/dgca-looking-at-mandatory-psychometric-tests-for-pilots-in-india-114032500763_1.html"]
I believe the DMT (Defence Mechanism Test) has been used by the Swedish military; it is felt that this eliminates individuals who are not up to the task before money gets spent on training them. Other slightly authoritarian countries possibly also test in this way. Yet overall I think that most informed opinion would query the value of any similar tests for commercial pilots simply on the basis of their validity. Many false positives would almost certainly result; indeed it would perhaps be that results needed to err on that side. This would simply debar many otherwise suitable individuals from the profession for very questionable reasons, at any stage of their career. We all can see that making flight crew pass through airport security and have, say, a jar of aftershave or a leatherman removed from their bag would go nowhere near preventing a pilot bent on destroying his/her aircraft; psychological evaluations would be equally futile. How often would they be undertaken - after all, a person's mental state of health can be very changeable over time. I would argue that peer concern/CRM/good open company management culture is a far more effective defence against this sort of act. That said, no doubt certain commercial organisations would see a good business opportunity in providing such services, aviation being perceived as a cash cow, and may well start pushing for this as well as some more nervous regulators wishing to demonstrate their grasp of the situation.
A professional pilot, military or commercial, goes through much rigorous selection and evaluation to get their licence and they then have continuous assessment of their ability and competency for the rest of their careers. No other profession comes close to being regularly and repeatedly assessed in such a fashion. That as final arbiters of safety of their aircraft they are made to endure humiliating "security" checks is bad enough; there is no need for this further knee-jerk reaction to what may or may not have happened in this instance.