Elma is being too smart. In a real DnD sesh, the party would either trust Kalos unconditionally and get backstabbed, or attack him as soon as he appeared from somewhere suspicious.
Eh it's fine. I don't think there's really anything else that hasn't been done before already. Trauma? Revenge? For the greater good? To stick it up to the system? It has gotten to the point where evil for the sake of evil is a refreshing trope.