If madness is one man’s illusion, perhaps sanity is also an illusion, but one shared by many instead of relegated to an individual. The psychotic simply perceives a different illusion or pierces the common delusion to reveal a deeper reality. Hence, the madness common to all gods.
Worshippers of madness attempt to spread the view of reality defined by their deity. Many are evil, or care not for the niceties of civilization, and enjoy the chaos and destruction they bring. A few might be called strange liberators, freeing creatures from oppressive realities, societies, or social stigmas…
A PC who embraces insanity, either refusing to participate in the collective mania or hastening the dissolution of the universe, can choose a divine paragon path, like this first one described here.