Considering he began as a hypocrite ( even a well-intentioned one), I think I would have been annoyed by Cotton turning out to be evil. How-eva, I do think there was an interesting, unaddressed theme inherent in his background as a child exorcist, which is really only the reverse-image of a child possessee. If his re-conversion/renewed faith meant that he reverted to his mental state during those years, and we went further with the idea of Nell's "demon" being a dybbuk-like single-form MPD which allowed her to speak out against the abuse she was suffering, now that might have been a neat-o Clash of Madnesses!