Actually, thinking about it. I see this playing out with less of the feel of "Fight Club" and more along the lines of "The Secret Window". Fight Club had a certain wow, that's cool feeling at the end, where Secret Window left you with a feeling of wow, that could really happen, poor guy just lost it trying to cope with life. The redeemable piece is the fact that the feelings being channeled to personality #2 were originally thought of and felt by personality #1 - Had he not lost it, personality #1 might've acted on those things anyway, but because he was a good person, he couldn't bring himself to do it.