of all the races that can be healers the only ones that have restriced ethos choices are arials. The helpfile sites only human and dark elven society could produce evil healers but I think there is an argument for evil arial healers. I mean so many evil arial mages, assassins, thieves, and so forth i think its not a huge leap to see an evil arial healer.

One could certainly make a case for evil arial healers. However, a deliberate decision was made to keep healers skewed good (a decision we took even further with the last healer revamp.) ICly, the premise is that the art of healing is by its nature a compassionate art, and therefore to be evil and choose the path of the healer is to be not only evil, but to have the potential for blurred and twisted ethics in a way only human and dark-elven societies can manage. A duergar who can be a shaman, for example, wouldn't exercise the languid and less direct evil that being a healer would imply - he just cuts to the chase in his evil. In our imaginings we suspect evil arials generally adopt something similar, a sort of impulsive and swift cruelty given their attitudes and short life spans.

This was mostly just a game-balance call, since the specific logistics of arial sociology/psychology hasn't really been spelled out yet in game lore.