Kinda weird to think in-universe that the bad guys explicitly call their side the “dark-side.” Paradoxically they don’t believe they are evil but they’re also conceding that they are evil. It makes more sense to stick with monikers like Sith vs Jedi. Like Republicans vs Democrats, either side is going to think the other side is demonizing. Neither would logically say they are evil or morally bankrupt themselves on their side of the fence. It’s not the most attractive way to recruit others. Imagine if Vader didn’t say scary things to Luke like “dark side” and just more things to try to screw with his head such as Obi-Wan being a liar. Saying you’re evil kinda cancels out anything else you say versus just appearing like you believe you’re in the right.