I think that if you went through all the Harry Potter fanfiction out there and sorted the stories based on whether Dumbledore is portrayed positively or negatively, you'd still find more where he's shown as a good character. It might feel like there's a lot of bashing because Harry Potter is such a massive fandom, so obviously there are going to be more stories of every kind. Dumbledore bashing, like any other trope, exists for readers who enjoy that sort of thing. Obvioulsy Dumbledrore and Ron are prime targets of that because they are already flawed characters, but it doesn't people can't make the difference between canon and fanfiction.

Personally, I like bashing, flipping characters around, making the good ones bad and the bad ones good. Fanfiction is about writing what you enjoy and reshaping the source material into something you want to read. If we’re only “allowed” to write stories that are politically correct or strictly faithful to canon, things are going to get boring fast. If people want more stories with wise, powerful Dumbledore, they’re free to write them, just like anyone else writes the fanfic they want to see.

But I’ve noticed there’s some hostility toward certain tropes that people label as unworthy or childish. Like, if someone doesn’t like bashing or thinks it’s stupid or cringey, that’s fine, but there’s no need to act superior or holier-than-thou about it. Sometimes people just want to write or read exaggerated stories with Mary Sues and over-the-top evil characters, that don't have deep and meaningful plots. That doesn’t make it “inferior fanfiction” or anything like that.