Outside the Web where everyone who keeps a blog can try his or her hand at reviewing, most "respectable" and "established" literary critics tend to be authors themselves. Sometimes we even have, say, an author/reviewer working on subject matter X reviewing a book on X written by another author (which means both authors are pretty much rivals of sorts), and yet the reviewer's opinion, even negative ones, is published anyway. It is pretty common for people with professional ties/enmity to review each other's books, rip them apart, and have the authors who got negatively reviewed retaliate with kind. I don't think those literary review sections of those papers or journals will go, "Oh Reviewer A hated Author K's last book, so she shouldn't read Author K's newest book!" 

So why is it that online reviewers seem to be subject to rules that "real life" reviewers don't seem to be bound by? One is not supposed to review a book by Author A after trashing Author's A previous book, because that will be "mean" and a show of "bias". One is not supposed to say mean things that can be translated to being a personal attack by the author. One is supposed to put aside book one dislikes because clearly, one shouldn't review a book that one doesn't "get". And so forth.

To be fair, online readers and reviewers impose rules on authors too. 

Still, all these rules do make me wonder why we need all these rules in the first place. I suspect it's a matter of control and power. By establishing rules, authors feel a measure of control, even if it's an illusionary one, over how the plebians on the Web is supposed to behave when it comes to their books. Likewise, sometimes readers and reviewers engage in power play too, rallying the numbers to form a internet tidal wave of "Will not buy your book! Because you disagree with me!" chain reaction that often lasts a week before we all move on to the next topic du jour. Sometimes, watching interactions between readers, reviewers, and authors online, I feel as if I'm watching some political strategy thingy in action!