Just to demonstrate that my ire isn't always about politics or law, I'm going to take both Scalzi and Harvilla to task for missing the, or at least one very important, point about negative reviews. Simply put, reviews aren't generated and don't appear in a vacuum… and a certain proportion of thoughtful negative reviews from a review source is the best demonstration of that source's trustworthiness.
A negative review is almost never the only review that reviewer has done. One learnt far more about — to choose a famous example — the perspicacity of Roger Ebert and Gene Siskel by hearing/watching/reading their negative reviews and defenses thereof. And that isn't just about nebulous "taste," either: A critic (or author writing a review, or author in general) had bloody well better have a conscious rationale for why certain "types" of works are outside their attention. It might be rational or irrational disdain; it might be humility in knowing how little one knows in some areas (one only wishes that more "critics" and "reviewers" of military and espionage fiction would acquire some of that… including too damned many "former military" and "former intelligence" people writing about radically different contexts unmerited by their own experience/scholarship); it might be bad experiences with crap (remember, Sturgeon was an optimist). It might even be so personal that the conscious rationale isn't for public consumption, like a reviewer who lives with PTSD.
More broadly, a single review is almost never the only review appearing in that review source. Here, I must genially disagree with Mr Scalzi on one point: PR people generally do not accept that reviewers are not just adjuncts of the publicity-and-marketing campaign, and especially not in more (self-) serious subsets of the arts. If they did, there would never be an embargo date on reviews. And this is where Harvilla's invocation of Krasinski and Anderson really fails: Simply by being prominent enough to be big fish in the small indie pond, Krasinski and Anderson are inherently part of the marketing-and-publicity strategy of others in that pond. <SARCASM> If you really want to see how it's done, try visiting the world of the young classically trained musician in nonacademic selective youth orchestras — presuming a very strong stomach and very high tolerance for posturing, bullshit, egos, entitlement and privilege, parents living through their children's achievements, outright sabotage, and temper tantrums. If you can shrug off the contemporary political news, you might have a shot at it. </SARCASM>
The well-considered negative review is a demonstration of trustworthiness on the part of both the individual reviewer and the review source. It doesn't even need to go as far as Ebert did about North in demonstrating that the emperor wasn't just naked, but was probably unable to spell "textile;" the gentle, considered thumbs-down is equally valuable in demonstrating that the reader of/listener to that review can have at least some trust that the reviewer hasn't been coopted and isn't just a cheerleader or relentless booster. And in the social media world with its unacknowledged benefactors, that's even more important. Objecting to a stale crust on that apple pie is not unAmerican.