PB, if I told you i'd have to...
BFB, i've done my fair share of research on said subject and human behaviour as it were. It is true that we are more complex than a psych test would allow us to think. However, I can safely say, used in the correct way they
are effective. As I stated above that includes the use of personal screening (interview). Though you assume you can 'fool' the process, I doubt that you are infact doing so. Candidates who have had interview and psych test coaching have obvious gives. It would surprise many just how obvious their techniques are, and thats not to suggest some coaching is bad. Considering the motivation questionaire, alot about ones persona can be drawn through patterns. Trying to fool this draws 'spikes'. You cannot answer what you think the airline wants, it will almost certainly catch you out. If you take the test on face value, sure, you could assume you are 'fooling' it. Above taken into consideration, I cannot speak for other many airlines who do infact have shonky questionaires they label 'psych' tests, which consist of little more than an IQ style test with some aviation questions whacked on.
Unless you are involved in the design of these tests, or the day to day use of them, I think its a little rich to completely rubbish them and their existence.