You don't have to be evil to be a villain. the definition of villain is someone who opposes the hero which Kisame is. Technically, Kisame would be an anti-villain. Anti-villain are light compared to a the pure villain as an anti-hero is a darkening of the hero. According to tvtropes, "The Anti-Villain is a villain with heroic goals, personality traits, and/or virtues. Their desired ends are mostly good, but their means of getting there are evil." Like Sasuke and most Naruto villains, he would be type 2 anti-villain. the world has made him to be evil. He doesn't want to be evil just to be evil. the world made him to be evil. If you want to know more about this then you ever want to know, google "tvtropes Sliding Scale of Anti-Villains"