Explain that I understand his is a mental condition like any other and respect they are honest about it and encourage them to seek help. If you exile them, like a lot of people would, you just reaffirm their beliefs that they are a monster, and they see no point in getting help or controlling them self, and then it’s your fault they got that way. Cause you told them it’s their fault for something that is in most cases a mental disorder.

I’d rather be friends with a person who fantasizes about murder but never kills someone, than know that my rudeness created a killer. But that’s just me.

And in the even you are suffering from this (not gonna ask for your privacy sake), then I encourage you to seek help and learn to live with it and manage it in a peaceful manner. We don’t choose our mental issues, we just choose what to do about them.