As evidence of unfairness, critics often cite a reporter's study that concluded one psychiatrist testified on behalf of the prosecution in 145 cases. The implication is that his opinions were assembly-line propaganda rather than thoughtful reasoning based on psychiatric science. But psychiatry is an imprecise science, largely a matter of opinion. If a hundred medical doctors looked down the same person's throat, all presumably would agree whether he had tonsillitis. But if a hundred psychiatrists interviewed a person with questionable behavior, there might be a wide difference in their diagnoses.
Some psychiatrists tend to err on the side of the prosecution, others on the side of the defendant.
Nearly two decades ago, the U.S. Supreme Court said psychiatrists should be free to testify. The court knew that prosecution and defense would present conflicting psychiatric opinions. Then, it would be up the the juries to decide which to believe. If there is a problem, it could be solved by punishing people for their crimes without regard to their state of mind. Not only would that make psychiatry a moot point, it could further the cause of personal responsibility.