Sometimes doing research brings one across an old case that overflows with wisdom.  From Flanders v. State, 156 P. 39 (1916) the Supreme Court of Wyoming Judge Beard:

And here, too, we should distinguish moral insanity, so-called, which is not insanity at all--at least not in the legal sense. It is well known that there are many depraved persons who, by continued indulgence in vice and crime, have so debased and debauched their moral sense and blunted their susceptibilities that the 'still small voice' of conscience no longer responds to the dictates of human or divine law, and fails to utter warning against the impulse of greed or passion. Sometimes the degradation is so complete that the most vile and detestible acts fail to bring the faintest shame or remorse to the perpetrator. This may be moral insanity, so-called, but, such depravity being induced by the voluntary maintenance of a conscious course of vicious indulgence on the part of the person concerned, and not by disease, there is manifest reason why such person should not be excused on the ground that his conscience fails longer to give a correct report of right and wrong. Moreover, though the man's conscience may break down in its proper function, such person cannot fail, if sane, to know how society and the laws of the state regard the act. For example, the most confirmed thief will hardly be heard to say that his conscience did not reprove him for the theft, so long as the defect in conscience is not the result of disease, but of his own willful pursuance of a course of dishonest conduct. Thus it is important to notice that the insanity which will excuse in law is the product of disease, and not of the defendant's own misconduct.