@Background Pony #1421
With villain adoration, it’s like this: we do know that stealing people’s individuality, turning the world into a maelstrom of chaos, or posing as someone’s fiancee for long enough for it to have disturbing implications while you plot to drain the life force of everyone who loves those you and your minions pose as are not nice things to do, but…

…it’s just a TV show. So you can play with them however you wanna.

Also, it’s cool to have an actual villain show up. There aren’t that many of them in this show. The adventure stories are always going to be more popular than the “lesson of the week for the little girls” stories to us older fans. One day the problem is “Twilight is anxious over sending a letter late,” another it’s “Fluttershy needs to come up with a nice way of telling the Breezies to go home,” another it’s “a monster escapes Pony Hell and begins eating the world’s magic, ending in a no-holds-barred magical deathmatch… wait, what?” The villains from those episodes stay in your mind more, they make you wonder how they got the way they are, what they might be like during downtime, if they could return, etc. etc. They’re just more compelling.

Sonata Dusk has a cute, fun personality. Is she really that bad, or someone who might soften if you just gave her a hug and ate some tacos with her? Or can you be funny and at the same time so evil that if only she had the chance she’d make Tirek look like a kitten? Would the rivers of Equestria run red even as she kept giggling, talking about lunch, and totally missing that your last words before she tore your heart out and ate it while it was still beating was sarcastic?

tl;dr Villains are cool. What they bring to the story is cool. We want moar.