Respectfully, I think you should look at this issue from two aspects, the narrator and the environment of the story.
It's convenient to ask ourselves ¿who that narrator is? Especially if it's a first-person narrator. Because your narrator can be an alien, a lamp, a fish, let's know. Or even someone of the opposite sex. And in all examples you must be aware that, well, you're who writes the story, the boss. But your narrator is the one who tells that story, even if it's an omniscient narrator. I think having this clear will keep you from confusing yourself later.
Because what happens when the narrator is also the villain?
But we must also have this clear as readers. We must be aware at all times that the character of a story, even if it looks like a real-life person, is actually just a literary construct, one sema. Speaking in semantic terms, a character is a communication vehicle that carries meaning. He's not that person he looks like in the real world. Therefore, the narrator of your story can say that that character is either acting in an evil, silly, or ambitious way, and it doesn't mean that you, as a writer, are criticizing anyone in real life.
However, it's amazing how people get confused. And sometimes the confused one is also the writer.
The environment of story also influences how evil is perceived. So, I want to say it once again, it's good to consider at this in the outline. Or at least reflect a little on that. Especially in creating a different culture. This civilization it may or may not be human. But we have to look at what the differences are. Because what we may think is an aberration to them may be totally normal.
A simple example: in the time of the samurai it was considered a serious offense not to bow when they passed. So, chac. And this for them constituted a code of honor. But what, chac, for something like that would we find it atrocious, wouldn't we? So, already in a human world you have differences in how life is perceived. Then that also influences the perception of evil.
Chac, chac. All wicked.