a preference and a standard are two different things
"This character is badly written because they are morally a bad person" is a preference, you dislike morally bad characters, but that doesn't mean the character is badly written, and doesn't mean the author should change them; it's subjective.
"This main character is badly written because they don't change through out the story" is a standard, it's an objectively true criticism; it's universally expected that a main character must change through out their own story, it's also constructive, the author can learn from it.
Some people try to push their preferences as standards mostly by telling whoever disagrees with them they have bad taste or low standards.
Some others try to shift the standard to make their preferences seem reasonable mostly by calling whoever dislikes what they like "a hate mongol."