Hi I’m a fantasy author.

If someone makes a species evil, it’s usually to justify the protagonist not needing to think too deeply about the nature of killing members of that species.

However, there is actually an entire genre of works that are like this. Sadly, the “evil species” in question are… humans(?). It’s called Xianxia/Wuxia/Cultivation and the general trend in this genre is that the cultivators (basically super powerful magic humans based on Chinese mythology) are all capable of doing good things, but often don’t because it’s better for them to be evil to obtain their goals.

For example: in a Xianxia book, it’s often the protagonist’s goal to become a true genuine Chinese immortal. There are a lot of ways of doing this, but oftentimes they may require you to do evil things.

A very stereotypical example in this genre is the human pill stereotype. A lot of people in these worlds often need to extend their lives artificially to get more power and to eventually find a more natural way to extend them. In order to do this, it’s common for a character to murder another person, take out all their bones, and crush them into a small pill they can consume, taking the lifespan of the person they ate and getting a little more powerful.

The entirety of this genre is likebthis, so if you’re interested in reading this kind of dynamic, I would pick up “Reverend Insanity”, “A Regressor’s Tale of Cultivation”, and “Renegade Immortal” in that order.