The consensus in criminal law circles feels settled: the insanity defense is a relic, rarely successful, narrowly construed by courts, and too easily exploited by wealthy defendants. Legal commentators nod along. Judges restrict its application. Legislatures keep tightening the standard. Everyone agrees the system works fine.
But that comfort should worry us. The better question isn't whether the insanity defense succeeds in court. It's what our reluctance to meaningfully engage with mental illness in criminal responsibility says about who we're actually punishing.
Consider the landscape. Most jurisdictions employ some version of the M'Naghten rule or Durham standard, asking whether a defendant knew the nature of their act or could conform their conduct to law. Sounds reasonable in the abstract. In practice, these tests create a narrow channel: you must prove not just severe mental illness, but a specific cognitive or volitional failure that meets a court's exacting threshold. The defendant bears this burden while prosecutors marshal expert witnesses to argue that yes, technically, the person knew right from wrong.
This creates perverse outcomes. A person experiencing active psychosis might understand, in some formal sense, that an act violates law while remaining fundamentally incapable of rational decision-making. A person with severe impulse control deficits stemming from documented neurological conditions might still pass the legal test. We've essentially built a system that asks courts to split hairs about consciousness while ignoring the substrate of mental dysfunction.
The real problem isn't that the defense is used too often. It's used far too rarely, and when it is raised, the bar sits impossibly high. We've allowed fear of a few high-profile acquittals to shape policy that forecloses meaningful consideration of mental illness across thousands of cases annually. That's not justice calibrated to reality. That's justice calibrated to our discomfort.
Criminal law traditionally rested on a bedrock principle: moral responsibility requires a functioning capacity to choose. That principle hasn't changed. What's changed is our willingness to honestly assess whether someone possessed that capacity. We've substituted procedural skepticism for substantive inquiry.
The consequences fan out. Defendants with serious mental illness cycle through prisons rather than treatment systems. Families watch loved ones navigate a criminal process ill-equipped to address the root pathology. Courts spend resources on adversarial battles over psychiatric causation that might better serve rehabilitation. And defendants themselves face sentences calibrated to crimes rather than culpability, landing in facilities designed for punishment rather than care.
This isn't an argument that all defendants claiming mental illness should walk free. Mental illness doesn't eliminate accountability. It should recalibrate it. A system with real teeth would distinguish between punishment, treatment, and public safety depending on diagnosis, risk assessment, and prognosis. We'd invest in specialized courts, mandatory evaluation, and dispositions proportionate to actual danger rather than categorical rules.
The consensus avoids this harder work. It's simpler to say the insanity defense is too permissive and leave it there. It's harder to build infrastructure for nuanced mental health assessment, to train judges in psychiatric realities, to accept that some dangerous people are also genuinely sick.
But consider what we're actually choosing: a system where mental illness affects culpability only in rare, perfectly documented cases. Where most defendants struggling with profound psychological dysfunction get processed through ordinary criminal channels. Where we measure success by conviction rates rather than whether the outcome matched the actual facts of responsibility.
That's not working well. It's just working quietly.