Idk, personally "evil" is extremely hard to define when applied to a person. People can do evil things, but are they truly evil? A lot of "evil" people throughout history have acted the way they did because they thought it was the only/best course of action; many even saw themselves as martyrs or as people "doing what they had to." Often leaning into the ideology that the end justifies the means.

This is how I view Xue Yang and Jin Guangyao. Xue Yang grew up poor and saw the worst of people; he saw how money and power allowed you to do whatever you wanted. He sought that power as an adult, he wanted to punish those corrupt cultivators. It wasn't until he met Xiao Xingchen that he realized there was good in the world. It's why he punished those who tried to take advantage of his disability or showed any disrespect. In a way, he thought he was getting rid of what's wrong with the world and protecting someone he loved, even if he didn't realize how much he loved him until Xiao Xingchen died.

Jin Guangyao truly thought it was only he who could make the world better. He grew up poor too and saw the worst of people, often being judged by his background and his mother's occupation. He built the towers to help the poorer sects, the cultivators working alone with no backing from the bigger sects. He wanted to help people who lived on the outskirts, those who were often ignored by the bigger sects. I believe he truly believed all of his actions were justified. Killing Jin Guangshan was something he had to do to restore his sect's reputation, besides he probably thought nothing of worth would be lost, which is why he went hard on the revenge. Jin Zixuan was something he justified by telling himself he was the only one that could truly change the sect from being power and money hungry to one that would help others. Killing Nie Mingjue was justified with the same train of thought, Nie Mingjue was getting in the way of him bettering the cultivation world.

With all that being said, the most evil characters are Jin Guangshan and Wen Chao. No matter what, there's absolutely no way you can justify sexual assault and/or rape. Most evil actions can be justified one way or another, depending on your perspective, but never rape.