You can largely blame Disney for that one. Lucas has been extremely explicit and direct that the dark side and the sith are a corrupting influence on the natural balance of the force and the universe the Jedi serve.
Lucas later retconned that, voluntarily, in a terrible Clone Wars episode involving an evil moon, a good moon, and a pompous magic family with a daddy figure lecturing his kids about how they each need to have just enough evil in their diet for a balanced breakfast.
Lucas later retconned that, voluntarily, in a terrible Clone Wars episode involving an evil moon, a good moon, and a pompous magic family with a daddy figure lecturing his kids about how they each need to have just enough evil in their diet for a balanced breakfast.![morshupls morshupls](https://www.hexbear.net/pictrs/image/c02af2c2-f4a1-4d6e-bf78-2e0565dc10ca.gif)