Kind-hearted and nice characters= Mary Sue ?!

[Tiffany Cheng]

A lot people seem to label any nice and kind-hearted characters as Mary Sue, some of them even outright hate them

Comments

[elbow568]

Usagi Tsukino from Sailor Moon

[lunalotte88]

Yes, there were some characters for whom I was surprised got a fair amount of hate. Sad. They were nice, and I could see myself hanging around them as friends if they were real, and they have realistic flaws.

Could it be connected to glorifying the not-so-nice but brooding, deeply tragic, sort-of-villain character (many of whom are great characters too)?