Psychology has uses in determining root motivations in individuals and cultures, there are basic responses to outside stimuli that are common between the majority of 'sane' subjects. That being said, the correlative data that makes a Rorshcach test useful is not a collection of 'correct' versus 'incorrect' answers, rather it shows the most popular response. If your definition of sanity is thinking and behaving the same as the majority of your peers and neighbors, then in the confines of a mental institution, the doctors would be considered the insane. Abstract pattern recognition is not something we understand well enough to diagnose a mental state from, if we did we could program a computer to recognize patterns as we do. Therefore, if correlated data is meaningless and it is the emotional response to the imagery that is important, than a completely randomized image would be the most useful for diagnostics. The ink blots themselves were the closest to a random image that could be created at the time, and a brilliant concept to begin with, but like many other great ideas, it was latched onto by others who did not truly understand it, but were content to use it for their own purposes. Draining the blood from people using leeches may have helped some recover from illness, but it was the enforced bedrest due to bloodloss and not the bloodloss itself that contributed. Just because something works does not mean it is working correctly, or for the reasons you may want it to.