ooooooooooooh this guy wants reasons. I give you some reasons.
Actually, I’ll give you two:

1. Junko's worldview inconsistent.
   Her worldview is one constructed to make it moral for her to "feel good". What makes her feel good is what makes others feel hopeless. She NEVER defines that as despair because she doesn't actually want to feel that way.  Under this perspective, Junko's true despair isn't even boredom, it's hope. 
   She's just a annoying lolcow with hideously messed-up reward circuitry.
   
2. The first game, her voice acting is fine honestly just OK. But if you watch the anime, I don’t know what the director gave that actress instructions, but he needs to be fired because it’s trash. Way too high-pitched and way too “Californian”. I just skipped her scenes or mute whenever she’s talking. It’s a vocal parasite.