'Evil' is all a matter of perception, just like 'Good'. Different kinds of people and societies all have their own ideas about morality. The Daleks from Doctor Who find hatred to be 'beautiful', like a thing of art, and are actually reluctant to kill anyone with 'pure' hatred, like the Doctor (and this is coming from a race of particle cannon-packing trash cans whose entire shtick is, literally, KILL, DESTROY, EXTERMINATE). The Liir from Sword of the Stars find any form of violence to be completely abhorrent, as they are all empathic creatures and feel the terrible storm of emotions and accompanying silence of someone's death. And so, in order to defend themselves from other races, some Liir have to voluntarily sever themselves from their society and become outcasts, since their high rate of PTSD from traumatic experiences in war would poison the whole collective. Also, rather amusingly, this race of peace-loving dolphin-like creatures are the most TERRIFYING race in SotS when it comes to biological warfare, as they see absolutely no problem with killing their enemies from a distance with wide-dispersal virus bombs on populated planets. Less emotional trauma than direct combat, that way.