“Nothing can be more slightly defined than the line of demarcation between sanity and insanity ... Make the definition too narrow, it becomes meaningless; make it too wide, and the whole human race becomes involved in the dragnet. In strictness we are all mad when we give way to passion, to prejudice, to vice, to vanity; but if all the passionate, prejudiced and vain people were to be locked up as lunatics, who is to keep the key to the as”