Cadence is not a bad person. So, I don't know why people write her in their fictions that way. She doesn't have much of a character in the show so writers have a lot of leeway I guess. I think she gets dumped on because she has had zero character development and her life is shown to be perfect. You can't even point out any of her likes or dislikes. The closest we've gotten to an origin for her is in the comics depicting how she met Shining Armor and fell in love in high school. That's it. There's a suggestion that she's a distant relative for a previous ruler of the crystal empire before they were killed by Sombra. There's also nothing about about she got her wings at such a young ago (yes, in high school). It would be interesting to have her and Chrysalis meet again in an episode. That would be fun.