Law in Failure: Do You Want Crazy? The Insanity Defense Sacrifices Public Safety to an Unscientific Fiction

 The insanity defense asks psychiatry to answer a question it cannot scientifically answer: whether mental illness deprived a defendant of sufficient freedom, rationality or self-control to deserve criminal responsibility. Psychiatry can identify symptoms, reconstruct behavior and estimate risk. It cannot measure free will, prove that an impulse was irresistible or determine how “causally compelled” one person’s conduct was compared with conduct produced by psychopathy, greed, rage or ordinary criminal motives.

The defense also confuses two different questions:

1. How morally blameworthy was the offender?
2. How dangerous is the offender, and how much incapacitation is necessary to protect the public?

Even if mental illness reduces moral blameworthiness, it does not follow that the offender is less dangerous. In some cases, the abnormalities offered as excuses are precisely what make continued incapacitation more necessary.

Judicial authority is not scientific validation

A court decision is an exercise of governmental authority. It is not an experiment, clinical trial or externally validated scientific finding. Repetition through precedent supplies neither a control group, known error rate, replication nor predictive validity.

Courts may choose a moral rule under which a person who cannot appreciate wrongfulness is excused. But they cannot transform that moral preference into a scientific fact merely by declaring it law. Any empirical assertion in a judicial opinion must be evaluated independently through real-world evidence.

The insanity defense is therefore best understood as a philosophical and moral doctrine using psychiatric terminology—not as a scientifically validated medical determination.

There is no scientific test for criminal responsibility

“Legal insanity” is not a psychiatric diagnosis. A psychiatrist can determine that a defendant probably experienced persecutory delusions. The psychiatrist cannot scientifically prove the additional propositions that:

• The delusions caused the particular criminal act.
• The defendant was incapable of responding to any competing motive.
• The defendant could not have refrained.
• The defendant lacked meaningful choice.
• His conduct was less voluntary than the calculated conduct of a psychopath.
• The correct social conclusion is acquittal rather than conviction and treatment.

The unreliability is measurable. A systematic review of field studies found that independent evaluators’ sanity opinions had a pooled Cohen’s κ of only .41, with a 95% confidence interval of .29–.53. That represents only fair-to-moderate agreement. Individual studies produced κ values ranging from .28 to 1.0. The evaluator selected can therefore materially influence whether the same defendant is declared sane or insane. Guarnera and Murrie, Psychological Assessment (2017)

The “irresistible impulse” or volitional branch is particularly indefensible. Forensic literature acknowledges that the line between an impulse that could not be resisted and one that simply was not resisted cannot be drawn reliably. Knoll and Resnick, Insanity Defense Evaluations: Toward Evidence-Based Practice

A legal conclusion with no objective measurement, no independent criterion standard and only modest evaluator agreement should not determine whether a proven killer is convicted or acquitted.

Mental illness often does not cause the crime

The existence of a disorder does not establish that it caused an offense. Peterson and colleagues examined 429 crimes committed by 143 offenders with serious mental illness. Approximately 64.7 percent of the crimes were classified as completely independent of psychiatric symptoms. Only 7.5 percent were classified as completely directly related to symptoms. Direct relationships were found in four percent of crimes involving psychosis, three percent involving depression and ten percent involving bipolar symptoms. Peterson et al., Law and Human Behavior (2014)

The finding does not mean that psychosis never causes violence. It means that the causal connection must be proved in each case rather than inferred from a diagnosis.

Severe mental illness by itself is also not among the strongest predictors of future violence. In a large prospective national study, historical, dispositional, substance-use and environmental variables were more important. Elbogen and Johnson, Archives of General Psychiatry (2009)

Psychopathy and antisocial characteristics strongly predict aggression and recidivism, yet they usually do not excuse responsibility. The legal system therefore treats one brain-based behavioral abnormality as an excuse and another as an aggravating danger without a scientific measure showing that one person possessed free will and the other did not.

That line is moral, not medical.

The cellmate test exposes the public-safety failure

Consider two offenders:

• A Mafia hit man who has committed 50 calculated murders.
• A person with paranoid schizophrenia, profound anosognosia, treatment refusal and a history of rampage murders committed in delusional “self-defense.”

Both are extraordinarily dangerous. But which would a rational person prefer as a cellmate?

Assuming the cellmate is not an assigned target, witness or obstacle, the Mafia hit man is the more rational choice. His violence is instrumental, planned and directed at selected targets. He generally needs an external motive to kill.

The untreated paranoid offender may perceive an innocent cellmate as an assassin, persecutor or participant in a conspiracy. An ordinary glance, whisper or movement can be incorporated into the delusional system and interpreted as a mortal threat. Violence committed in “self-defense” against an imaginary attack does not require an actual dispute or criminal order.

Therefore:

• The hit man may have the greater demonstrated capacity for calculated killing.
• The untreated paranoid rampage murderer presents the greater immediate danger to an arbitrary nearby person.
• Neither is an acceptable candidate for ordinary release.
• If forced to choose, a rational cellmate would choose the hit man, provided there were no reason for the hit man to target him.

This is not a claim that people with schizophrenia are generally violent. Most are not. It is an individualized assessment of a person combining repeated serious violence, active persecutory beliefs, anosognosia and treatment refusal.

The evidence supports focusing on those particular factors. A 2025 systematic review covering 203,297 people with psychosis found that criminal-history factors were the strongest predictors of violence, with a pooled odds ratio of 3.50. Treatment-related factors were protective, with an odds ratio of 0.54. Whiting et al., British Journal of Psychiatry

A review of 110 studies involving 45,533 people similarly identified criminal history, hostility, poor impulse control, substance misuse and medication nonadherence as important risk factors. Witt, van Dorn and Fazel, PLoS One

Persecutory delusions become especially relevant when accompanied by anger. In a prospective forensic cohort, suspiciousness and persecution were associated with violence, and anger statistically explained 84 percent of that relationship. Coid et al., Journal of Forensic Psychiatry & Psychology

Lack of insight is also a major driver of medication nonadherence, which in turn increases relapse and hospitalization. Higashi et al., systematic review, Therapeutic Advances in Psychopharmacology

The insanity doctrine makes a fundamental category error: it treats impaired appreciation of reality principally as a reason to reduce responsibility when, for public-safety purposes, the same impairment may increase the need for secure custody.

Insanity acquittal usually produces custody—but that does not validate the defense

The insanity defense is raised in approximately one percent of felony cases and succeeds in about 26 percent of those cases—roughly one successful insanity disposition per 385 felony cases. Callahan et al., Bulletin of the American Academy of Psychiatry and the Law (1991)

It is also inaccurate to suggest that every insanity acquittee simply walks free. Federal law requires immediate commitment after an insanity acquittal. For violent offenses, the acquittee bears the burden of proving by clear and convincing evidence that release would not create a substantial risk. Conditional release can require treatment, and noncompliance can result in arrest and recommitment. 18 U.S.C. §4243

In Missouri, 85 percent of insanity acquittees remained under commitment five years after acquittal and 76 percent remained under commitment ten years afterward. Linhorst, Journal of the American Academy of Psychiatry and the Law (1999)

In Connecticut, 16 percent of acquittees were rearrested after final discharge from Psychiatric Security Review Board jurisdiction. Prior conditional-release supervision significantly reduced later arrest risk. Norko et al., Behavioral Sciences & the Law (2016)

These commitment systems protect the public to a degree, but they do not validate the underlying insanity verdict. They are separate mechanisms created to repair the obvious danger produced by acquitting someone who has committed a serious criminal act.

The remaining structural problem is that an insanity acquittal can eliminate the ordinary criminal sentence. Continued confinement may then depend on proving both current mental illness and current dangerousness. Acute psychosis may remit in a hospital, while the person’s violence history, antisocial traits, anosognosia, substance use or likelihood of stopping treatment remains.

A temporary clinical improvement should not erase the incapacitative consequences of repeated murders.

Abolition without a replacement can also fail

Merely deleting the insanity defense is insufficient. After Montana abolished it, insanity acquittals declined, but incompetency findings and dismissed charges increased. The legal system shifted defendants into another procedural category, sometimes allowing severely disordered defendants to avoid both prison and forensic hospitalization. Callahan et al., Psychiatric Quarterly (1995)

The necessary reform is therefore not deletion alone. It is replacement with a coherent system that separates proof, treatment and public protection.

A scientifically defensible replacement

A rational system should contain the following elements:

1. Preserve the prosecution’s burden. The government must prove the prohibited act and every statutory mental-state element. If a disorder genuinely prevents formation of a required specific intent, the prosecution has failed to prove that particular offense.
2. Abolish the separate insanity excuse. Once the act and ordinary mens rea are proved, an unmeasurable psychiatric opinion about moral wrongfulness or irresistible impulse should not convert guilt into acquittal.
3. Use a truthful verdict. A suitable verdict would be “guilty with severe mental disorder” or “criminal act and mens rea proved; secure psychiatric treatment required.”
4. Set the custodial floor according to the offense. The minimum period of incapacitation should not be shorter merely because the offender was psychotic. A person who commits repeated murders should remain securely confined according to the seriousness of those acts.
5. Determine the place of confinement clinically. A person requiring hospital-level care should receive treatment in a secure forensic hospital. If hospital care is no longer necessary but the criminal sentence remains, custody can continue in a correctional psychiatric unit or prison with appropriate treatment.
6. Do not confuse symptom remission with elimination of risk. Release decisions must consider prior violence, persecutory anger, psychopathy, substance use, insight, adherence, access to victims and weapons, and behavior during graduated privileges.
7. Require sustained evidence before release. Brief improvement in a controlled hospital does not demonstrate safety in an uncontrolled community. Release should follow sustained stability, progressively less restrictive testing and a realistic adherence plan.
8. Use enforceable conditional release. Medication monitoring, substance testing, supervision, victim restrictions and rapid review of serious noncompliance should be available where individually justified.

Conclusion

The insanity defense is not a scientifically validated determination of absent responsibility. It is a moral doctrine resting on psychiatric opinions that have no objective measure of free will, no reliable test for irresistible impulse and only fair-to-moderate agreement among evaluators.

Mental illness frequently does not cause an offender’s crimes. When psychosis does contribute to violence, that fact may reduce moral blame under some philosophical theories, but it does not reduce the public’s need for protection. An untreated, anosognosic paranoid offender who repeatedly kills innocent people in delusional self-defense may present a greater danger to an arbitrary bystander than a calculating professional killer.

The criminal law should not transform the very characteristics demonstrating extreme danger into a route around conviction and proportionate incapacitation.

The scientifically and logically defensible rule is straightforward: prove the act and required mens rea, provide secure treatment for genuine illness, and determine the necessary custodial term from the harm committed and the demonstrated risk—not from an untestable claim that one offender lacked free will while another possessed it.