I thought I'd share my insights on why some characters are bashed.
Perhaps, bashing of a character comes because one doesn't understand where a character is coming from. Paraphrased examples (from Harry Potter, as it is one of my main fandoms):
"I don't know why Molly treated Fleur so badly!"
"I cannot UNDERSTAAAAAND whyy Peter betrayed his friends! I just don't get it! I would NEVA do that!"
"I don't know why Lily didn't give Snape a chance after his apology! She didn't understand his situation! She was a s--y friend!"
I can easily understand why the above characters acted the way they did, so I don't hate them for it. People often oversimplify grey characters. If you were in these characters' shoes, how similarly or differently would you have acted?
I have also been wondering this: Does adoration/worship of a particular character often go hand-in-hand with hatred of another character?
Ahhh...the joy of double standards.
I guess humans are just plain biased. (Not that I'm immune...)