Ron is the most bashed character in Harry Potter fanfiction and is not even close, he is even bashed in the Hinny fandom, a pairing where he is not an obstacle. It’s mostly due to the movies butchering his character and partly due to Dramione and Harmione fans trying to find a way to break up Ron and Hermione.

It’s idiotic, really, how much he’s bashed.

After Ron the most bashed character is Dumbledore, then Molly comes third.

Dumbledore is bashed because his canon version is incompetent as fuck, so the people that can't accept Dumbledore as incompetent prefer to rationalize it with him being an evil mastermind.

Molly is bashed for being an overbearing mum and easily swayed by the press, then fanon liked to make her Dumbledore's dog. Ginny tends to be bashed because of shipping as well. Hermione is bashed in the Indy fics but not as much as the others.

As for the least bashed characters are in this order: Harry, Luna, Neville, Fred and George. I rarely find any bashing of them.

 

Dumbledore managed to convince the most powerful Dark wizard in history that an 11 year old was his prophesized nemesis, using a giant chessboard, some flying keys, a logic puzzle, and a funky mirror.

 

Luna isn't often bashed, but I feel a lot of that's because the fandom's unsure how to treat her - whether you write her as just insane, or as a seer, or as a cannibalistic polar bear, you'll get people complaining regardless, so it's easier to just sidestep the issue and avoid her in a fic. This is pretty easy to do, as she's a year below Harry, in a different house, and is only vaguely tied to them initially through friendship with Ginny.

Neville is often lionized, rather than bashed.
And I'll be honest, I'm not sure how much you can bash him - he was brave but incompetent (until he wasn't), and just making him cowardly instead just kind of breaks his character.
"Thanks for suggesting I use a new wand, Harry!" yelled Neville, as he rode his venomous tentacula patronus into the clouds, Bellatrix's head dangling from his belt, "I'm the second most powerful wizard in Britain now!" might sound like an exaggeration, but it's pretty close to how I often see him portrayed.
I used to think he should be bashed more, because I felt it incredibly lazy that just patting someone on the shoulder and saying "you're a decent bloke, Nev, I'm glad to know you" and giving them a new wand suddenly makes them actually a large player in a story. I still feel that, to be honest, but I can put it aside for good writing, or I can set a fic aside if it's also bad. If you want Neville to be a large part of the story, don't just overwrite canon like that.

Whether the reason for the strong Neville uplift is a lot of fanfic writers see themselves as bumbling incompetents with overbearing and abusive blood relations isn't something I'll dive into, as I'm not a therapist.

I think you're right that Fred and George don't get bashed much, and I think the trick there is there's not much you can realistically do to weaken them, without just destroying parts of their character? They build a successful business despite dropping out of school, they're relatively friendly chaps who most people don't dislike, except the Slytherins; but that is where I've seen them 'bashed'.
In that they're twisted into psychopaths who torture people for fun. Constant cruel tricks on the poor little Slytherin firsties, switching foodstuffs to allergens and the like.

 

The only context where I've ever seen Neville get bashed is when he's the BWL instead of Harry. Usually depicted as a consequence of the fame going to his head from staying in wizard society rather than growing up in obscurity like Harry.

If we put aside the question of how much established personality a character needs before it becomes fair to call an interpretation bashing; I don't think I've ever seen anyone bash Daphne. She's at the absolute worst a standard Slytherin mean girl. Which makes sense, why would a writer bother bashing her when Pansy's right there?

On the subject of Harry's more common love interests I'd say the scale from most to least bashed goes:

Ginny>Hermione>Cho>Pansy>Tonks>Luna>Susan>Daphne>Fleur

Admittedly Ginny, Hermione, and Cho are the only ones who ever get bashed for pairing reasons, whereas Pansy and Tonks are usually just package deals with general Slytherin and Order bashing. Has anyone ever read an outright negative depiction of Fleur though, because I can't recall any?

 

I've definitely seen some where her arrogance is played up and she's made to act like a bitch, but it's usually in an "Oh yes mean pretty lady, please do step on me!" sort of way. I don't think we see enough of her in canon for authors to actually hate her, and she's distant enough from the plot that as long as the author isn't interested in her she just won't appear in the fic.

 

He's incompetent as fuck at being a school headmaster. He repeatedly endangers the lives of students in order to draw out a terrorist, hires and keeps several incompetent/abusive teachers (e.g., Snape, Hagrid, Trelawney, Lockhart) for reasons unrelated to their aptitude for the job, shows blatant favouritism to certain students, and knowingly allows terrorists attempting to assassinate him attend the school to the extreme detriment of other students (e.g., Malfoy.).

He's great at creating the conditions to bring about the downfall of dark lords, but not at much else.

I don't think that any characters deserve to be bashed, but there are a hell of a lot of valid reasons for HP characters criticise and dislike Dumbledore, and he really shouldn't be in charge of children.

 

Abusive teachers? Endangering the lives od students? Outta here with your muggle health&safety bullshit.

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Miscellaneous Plots Chapter 6: Hogwarts School of Danger and Disasters, a harry potter fanfic | FanFiction

 

I guess the big problem with Dumbledore is just that there's no clear division between what he should know about and what he shouldn't, so it's hard to forgive the times he misses something important in light of all the stuff he is aware of.

He knows Legilimency, and yet Death Eaters are able to hide under his nose for an entire year twice without him being the wiser. He knew Quirrell was sketchy from the start despite the man having been a normal teacher in the past, and yet Peter and Crouch slipped right under his radar. Maybe Crouch knew Occlumency, but I understand that's also supposed to be able to combat Veritaserum. Crouch was unable to do that, so it doesn't fit. And there's little reason to think Peter knew it either.

He knows Moaning Myrtle was killed by Slytherin's monster, and yet it didn't seem to occur to him that her bathroom would be a good starting point for an investigation. Even if he couldn't open the chamber, he could have placed protections around the bathroom.

He knows Harry and Snape go together like oil and water, but just assumes they'll cooperate with Occlumency lessons even though he never does anything to enforce good behavior towards Harry on Snape's part, nor does he properly explain the importance of the task to Harry because of his self-imposed communication blackout that year.

And so on. Dumbledore has character flaws we know about relating to his guilt over Grindelwald and resulting refusal to trust himself with power, his secrecy and mistrust of other people and all that. But some of his lapses don't relate to those flaws and are just there because a Dumbledore who's as competent as he's supposed to be (and IS in a ton of other cases!) would halt the plot in its tracks.

You're not supposed to attribute to malice that which can be explained by stupidity, but when someone is stressed to be anything but stupid as often as Dumbledore, you're forced to fall back on malice.

 

Be fair. Why the hell would Dumbledore ever try and mind read his student's pets?

You could probably spin that as just Dumbledore being polite to Moody. The real Moody would likely react badly to even his closest friends trying to use Legilimency on him and, with Dumbledore having no reason to be suspicious, Dumbledore never attempted it.

 

I'm talking about before Harry's parents died. They suspected there was a spy in the Order and yet Dumbledore couldn't figure out who it was.

 

In regards to Dumbledores actions is once you start with some of them, they sort of keeps piling up due to him being more of a plot device and can't exactly be consistent.

Where do you end it once you look at him critically, Sirius situation, Dursley abuse, state of magical britain, the enviorment in the school he is in charge of? All of them can be argued for to varying degrees of sucsess by a person and once something sticks, the rest follows.

Harry has legitimate issues between OotP and DH and they weren't resolved at all, Harry in book 5 goes from having Dumbledore flat out giving that he is going to be open to book 6 lying to him in his face while continue to claim he is Dumbledores guy 100%. Why Harry would have trust in Dumbledore after that isn't revealed, nor do we see it.

 

I think some form of adult incompetence (or at least inattention) is a prerequisite for the YA genre. You need the children to end up on dangerous adventures where there are no grown ups to save the day, and that is hard to explain if the parents, teachers, authorities etc. are doing their job.

(My favorite way stories create this dynamic without bashing is: the adults are not dumb or evil or uncaring, but they are tired, busy, overworked and dealing with their own problems and only have so much time and energy to spend paying attention to what the children are up to. Meanwhile, the children are smart and precocious and getting up to all kinds of things the adults don’t know about, and eventually stumble their way into an unexpectedly dangerous situation and have to fight their way out.)