(For previous posts in this series, see here.)
Many people are suspicious of the insanity defense, suspecting that it is abused by unscrupulous criminals and their lawyers. The fact that psychiatrists and other experts can be found to argue both sides of the case adds weight to the suspicion that there is no objective basis to many of the claims of insanity.
This problem arose when the grounds for the insanity defense was loosened from the strict M’Naghten rule. In a 1954 court decision Durham vs. United States, a US Appeals Court extended the reach of the insanity defense beyond cognitive incapacity and said that “The rule we now hold is simply that the accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect.” (Steven Pinker, The Blank Slate, p. 184) As a result of the Durham precedent, there was a proliferation of expert testimony on both sides to argue the question of whether the accused did in fact have a mental disease or defect and whether the act that was committed was the product of that defective mental state, and thus not truly ‘free’.
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