So, too, have people who are deemed insane.  To be sure, the "tests" for insanity have varied over the centuries, but people who are mad, or to put it in modern terms, affected by severe mental illness at the time of the commission of their crimes, have not been considered responsible for their conduct if their capacity for rationality was seriously impaired.   Crazy reasons are not just bad reasons; they are reasons that arise from fundamental defects of the mind.  The law can punish the foolish person, but it ought not punish someone who was incapable of forming good reasons through no fault of his own.

But does the federal constitution provide a right to the insanity defense?  Many who claim it does suggest that it can be found through the application of substantive due process within the federal constitution.   Maybe so.  But is the insanity defense truly a substantive right rather than a procedural one?  

For many years, the Supreme Court has tried to adequately delineate what is substantive versus procedural under the Teague doctrine, which deals with retroactivity under federal collateral review.  Under this doctrine, new rules of criminal procedure are not retroactive unless they are substantive or watershed rules.  The Court has said that watershed rules are rules that implicate the fundamental fairness and accuracy of a criminal proceeding.  Or as Justice Harlan, the author of the Teague doctrine noted, these are rules that are "implicit in the concept of ordered liberty." The quintessential watershed rule that the Court has pointed to repeatedly is the right to appointed counsel in Gideon.  The right to appointed counsel is not just a procedure but a fundamental right essential to a fair trial.  It is necessary to protect the innocent and to safeguard individual liberty from the awesome power of the state. 

The same can be said of the insanity defense.  It is deeply rooted in Western legal traditions, and it ensures that only those who are rational agents are punished.  It safeguards those who are not responsible for their conduct due to no fault of their own.  A system of justice that convicts someone who is so out of touch with reality that he cannot reason sensibly is an unjust one.  He cannot be guided by the law because he is insufficiently governed by its reasons.  To be sure, Teague commands no finding of a federal constitutional right to the insanity defense, but it can guide how such a right can be conceptualized as a procedural right.  The ability of defendants to present a defense of nonresponsibility is implicit in the concept of ordered liberty because personal responsibility is a bedrock principle of our justice system. 

Some jurisdictions may claim that proof of mens rea is sufficient for a finding of responsibility.  But intending to do something, even if it is proscribed by law, does not adequately inform us of its wrongfulness or a defendant's capacity for rationality.  Just about all human actions are intended but what we care about is why they are done.  Even children understand this notion.  Why someone acts informs us of their motives and reasons.  There is a world of difference between killing someone to gain his wallet and someone who kills under the delusion that the victim is the devil who has come to harm his children.

In short, reasons matter.

Any discussion about the insanity defense invites skeptics who complain about defendants who malinger or flaws within the formulations of the defense.  Those are all worthy concerns but they do not vacate the moral principle that people with serious impairments in their rational capacity are not responsible agents.  If they are not responsible they are not deserving of punishment.  The Kahler case is about the right to present that essential fact to the jury for consideration.