Against the backdrop of this thread, everybody reading would know exactly what AlanF, Outlaw and myself meant when we described Robert King as insane.
I'm the first to admit I don't know what is going on for this man from a mental-disorder perspective. However, it's worth defining the term "insane": From a legal perspective, it is used as a defense because it means the individual was assessed (usually by a psychiatrist or forensic/clinical psychologist) as so severely mentally disordered that they are incapable of taking responsibility for their actions - especially regarding any harmful behaviour to themselves or others that results in the breaking of the law.
Here is an excerpt from the sixth edition of Synopsis of Psychiatry by Kaplan and Sadock (1997):
"According to criminal law, a socially harmful act is not the sole criterion of a crime. Rather, the objectionable act must have two components: voluntary conduct (actus reus) and evil intent (mens rea). There cannot be a mens rea if the offender's mental status is so deficient, so abnormal, or so diseased as to have deprived the offender of the capacity of rational intent. The law can be invoked only when an illegal intent is implemented. Neither behavior, however harmful, nor the intent to harm is, in itself, grounds for criminal action." p. 827
Now, the tricky part is determining whether a mentally-disordered individual was also legally insane at the time the actions were committed. Extreme examples often help get the point across: Was Hitler insane or "just" evil - in other words, although probably personality disordered (e.g. psychopathic), to what extent did he display rational intent as defined by the law?
As I see it, the question is not whether Robert King has some sort of perosnality disorder (I'd guess he does). The question is, to what extent does his mental illness preclude him taking responsibility for any behaviour stemming from his beliefs?