Being insane does not preclude him from being a racist.
He clearly is a racist.
Being insane does not preclude him from being a racist, or a sexist, or an Anglophobe, or a folk singer.
It is irrelevant to all those things.

Being insane does not in any way lessen the danger of his cause being acted on by others of similar opinions, nor does it increase the danger.

His insanity makes everything else irrelevant.
He only did it because he is insane.
(According to the court psychiatrists who have spent months assessing and diagnosing him.)