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For Absol here, I wanna add there's actually several reasons why Dark Type makes sense for it and "It's only Dark cuz people perceive it as bad" isn't actually why Absol is Dark Type.
It has a yin yang for a face, so Absol acting heroically while being Dark is the whole point. It being a symbol of disaster means it has a theme of bad luck/misfortune that other Dark Types like Murkrow have. It has a Grim Reaper scythe horn because people die in disasters, but the Grim Reaper only looks scary and is really there to guide and to help you.
Absol's basically just Dark because it senses negative energy/bad luck in the same way Vaporeon is Water because it senses the approach of rain. It knows when bad doomsday shit is about to go down.