For most people, good and evil are just concepts to align with, not choices. Yet doing good or evil can still be a deliberative choice. For instance, a Paladin lives for his ideals, while an evil Priest might cause pain and fear to please a God. Neutrals often simply lack recognition of either faction.
Perhaps having seen too much of the Demons' ways, Chen Feng already harbors some shadows, and thus has an instinctual aversion towards those Chaotic Evil creatures.
It is precisely because of this that he is eager to claim this plane. It's like a sieve, helping him filter out the Chaotic Heretics, leaving behind only a few Guardians of Order.
The numbers won't be too many. Out of a thousand Demons, perhaps only one extraordinary being with a nature of Order will be born. But for Chen Feng, that's enough since it's essentially a gift—getting powerful subordinates without expending any energy or wealth.
