The truth is that "his readers" (my emphasis added) consider him credible while you and other readers will not.
This is a really important point. For it emphasizes a certain beginning rather than an end.
The fact that those divisions exist translates into economic considerations—i.e., those divisions mark the equivalent of demographics (for either sales or marketing). So there is moneyed interest and all sorts of pressure which keeps them, and the attendant opinions and reasoning, intact.
What I find really interesting are the guiding questions/assumptions of reviews and, particularly, debates between reviewers, since for any good debate you have to force yourself into another's position and perspective to really argue effectively.
I realize that this doesn't really fit the word as people use it, but for me a good example of a "subjectivist" is David Griesinger, whose psychoacoustical studies force you to pay attention to the minutia of what you perceive (almost like a good debate with yourself). Psychoacoustics isn't
only about the limits of perception.