Saying "I don't like that this character did this thing," or "I don't like the direction the story is taking," or "I think the story is inconsistent" is one thing. Saying "I think that a character should have had a completely different arc that would have negated the character's entire purpose in the story, and I will argue against anyone who says otherwise" is quite another thing entirely.
Also, I'm incredibly disinterested when people try to shoehorn in "morally justified" arguments, even if veiled enough to skirt on the right side of the ban.