Kayle vs Morgana is a very grey area but I want to make it clear that Morgana is not canonically evil. In fact, judging by quotes and backgrounds alone, Kayle is pushing the boundaries between righteous and tyrannical.
Kayle's quotes are all about judging people:
"Your time has come"
"An eye for an eye"
"You shall be judged"
Morgana's quotes at first seem evil and threatening, but if you know about the background between her and Morgana it seems to be more of a warning, like "Even if you ally yourself with Kayle she will step on you if you stand in her way".
"Share in my torment"
"You too will be judged" (I am almost certain she's talking about Kayle doing the judgement, not herself)
"Not all angels are good" (Again, I don't think she's referring to herself, but Kayle)
So even if you don't believe Kayle is a tyrant who is in fact so self-righteous and careless that she is on the borderline of being "evil", I also don't think Morgana is evil. At the very most, Morgana is a deserter or traitor, but not for selfish or evil reasons. She is one of the few of her own kind who fought against what she perceived was tyranny.
EDIT: I wasn't really meaning to make claims that Morgana or Kayle were good or evil, I simply meant to say that there is no lore or mod quotes or anything that canonizes Morgana as being evil.