You ought to take a look at the meaning of the words "objective" and "bad". I don't think they mean what you think they mean.
Opinions on literature can't be objective because it's impossible to completely remove emotion and personal bias of the judgment of a literary work... Which is needed for an objective judgment. For something to be objective, it has to exist independently of perception or an individual's conceptions- Even in a less broad sense, people will disagree on what makes a work good or bad, or how well a certain trope was executed within that work- an objective standard for entertainment is pretty damn impossible.
Bad just doesn't mean "unable to be enjoyed", plain and simple. There's no contradiction there. There are awful, awful works that I can have fun with by just mocking them out loud while reading. In LB's case, it's more that a single part of it (refrain) was midly entertaining while the rest either sucked or badly sucked, so the work still goes into the "bad" category for being unable to meet the subjective standards I set for a "good" VN, even with a good part.