Let's see here...
Ahri at least WANTS to not kill people
There's no indication Cass had magic before she got bitten by a statue, and there's not really anything to state she's used her newfound powers for evil; on the contrary, she has used them to take out at least one serial killer.
Lulu has no canon lore.
Lux? Okay, I guess she was involved in Sylas's escape, but she hasn't done anything bad herself, certainly not intentionally.
Morgana has no canon lore.
Ryze? The fuck? Ok, I guess there was that one tribe, but greater good and whatnot. Sometimes you have to choose between bad and worse.
I can't condone imperialism, but Swain at least thinks he's doing the right thing by uniting the world in preparation to fight a greater threat.
Syndra and Sylas are victims of circumstance. I can't really fault them for being humans and therefore emotional, especially after years of imprisonment and facing certain death.
TF is a scoundrel and thief, no doubt, but he's nowhere near as bad as Brand or Malz.
Veigar has done nothing wrong, ever. Hell, like Cass, he kills evil people.
Zyra isn't really something you can apply such a human concept as morality to.