Why psychiatry needs to be removed from the courtroom
Both psychology and particularly psychiatry lend themselves to a-priori blanket judgments of individuals, removing credibility from their legal claims without in fact verifying the specific validity of their allegations--thus undermining the essence of the judicial process at its very beginning. It is far all too easy to use psychiatry as a weapon to invalidate unfavorable witnesses or claimants in the courtroom, before an opportunity has been given to even present their claims. While this might save opponents a great deal of time and money, it certainly goes without saying that violates completely the principle of equanimity and justice before the law.
And this is precisely the problem with psychiatry; it easily lends itself to a blanket value judgment on 'personas': the character, personality, ideas and notions of an individual. The field is tainted with too much social power as a result of its the broad value judgments which afford it over an individual--judgments which are generally speaking entirely subjective and variable according to the nuances of the culture, family dynamics, and personality traits in which they exist.
A good contrast can be made to that of neurology.
An neurologist is much more akin to a dentist than to a psychiatrist per se; their focus will strictly reside on the mechanics of the brain; on its internal functioning or 'chemical processes'. Though it is still a relatively young science, it stands in marked contrast to psychiatry given that it does not reside on an evaluation of the 'persona' but rather on the mechanisms underlying their cognitive processes. When you chip your tooth, you go to your dentist, and have it fixed; there's not a second thought to it because it is a purely functional procedure absent of value judgments of the individual or their beliefs. Like kicking a car's tires or checking its carburetor, the neurologist will assess whether the appropriate parts are in working order; correct dopamine levels (as brake oil), appropriate neurotransmitter firings (as a spark plug) and so forth.
It is actually interesting to point out that in those 'gray areas' where psychiatry operates, so subject to a wide degree of interpretation, that are precisely when psychiatry is most needed--but at the same time when it is least applicable to the court room. Debates of interpretation in the court room must be based only the rational and critical evaluation of the evidence available, rather than on a-priori value judgments of the individuals making them. These procedures hence by definition must be subject to rigorous logical and evidential debate, whose outcome cannot be predetermined by a 'personality profile assessment'. It is only upon the outcome of that finding, that a psychological assessment might be made; but it certainly cannot preced and preted to make statents of fact prior to when these are actually proven.
On the other hand, it is when psychiatry is most certain of its claims--the 'lunacy' of an individual, for example--that it is least needed in the courtroom, as its validity will be patently visible to all who participate in the judicial process, thus failing the need of a psychiatrist to verify such assessment. Obvious claims of fact usually do not require professional expertise to be validated.
It is to be noted that specific claims are subject to a highly variable a-priori interpretation in the public eye, according to the surrounding circumstances and context in which they appear. Truth is not 'out there', and even the same facts are subject to a wide latitude of varying interpretation relative to its shifting background. For example, while the claim that 'the government was spying on me' would have sounded like the rantings of a paranoid schizophrenic in 2005, after the Edward Snowden revelations, such claims became 'de rigur' in the general public and the intelligentsia. It was not so much that the claims of the individual had changed (or their validity), but rather their context had been radically altered. As a result of Snowden's courageous disclosure, he made these claims to not only sound reasonable, but in fact 'to be expected' as a pattern of behavior from government and its public institutions. What was anomalous became the social norm.
As a matter of judicial practice, it is commonly seen that witnesses will readily be subject to bribery, extortion or threat, thus have a higher likelihood of lending themselves to provide false testimony against a defendant in the courtroom. While paper-trails, videocameras, and other physical evidence as fingerprints and DNA evidence can be regularly used to invalidate such false testimony, it goes without saying that the incidence of 'poor data' due to a falsified testimony will have a much higher likelihood occurring due to fraud than to mental illness.
Far worse, from a professional's point of view, is when the psychiatrist or psychologist allow themselves to be bribed so as to use their enormous social power in order to invalidate claimants or evidentiary testimony in the courts. It is far worse than the case just described because the debate over the specifics of particular point or testimony aren't just being undermined, but (again) the entire testimony or claim of an individual is being discarded prior to the assessment of the validity of such claims. The inherent due process before the law, as reflected in the practice of habeaas corpus, is being violated due to criteria entirely outside the courts domain; and in effect shifting the court's social responsibilities on a third parties which by definition lack the constitutional guarantees which safeguard all courtroom procedures.
(It should be the practice of the court to permanently remove the right to practice medicine of any psychiatrist exposed of such notorious practice.)
The only medical professional related to cognition that should be allowed to provide any testimony is that of the neurologist.