I have thoughts about this, and those thoughts make me want to drink alcohol in large quantities (and they also make me very, very glad that the authors I discuss are dead/too rich to care what I think). So instead I'm just going to talk a bit about negative reviews in general and "being nice."
Books are products. They are not an author's baby. A baby is a living, breathing person and that metaphor is tired and silly. It's a product an author has worked their not-literal guts out to create, but it is still a product that I have purchased. Since I have purchased a product, that makes me a customer. It is unwise of an author to come to a customer with any amount of YOU'RE WRONG YOU DON'T UNDERSTAND MY BOOK YOU ARE A FOOL! A FOOOOLLLL! MY ART IS KING!
Goodreads is a social networking site, not a professional reviewing site, and most of the users are regular readers. The vast majority of book blogs are also hobbyists who do not get paid to write reviews. We are therefore under ZERO, literally ZERO obligation to include happy thoughts or censor unhappy thoughts, no matter how rude, vulgar, mean, negative, or "not nice" the author may think the reviewer is being. It is eyebrow-raising for an author to invade the space of an unpaid, non-professional reader (i.e., customer) and berate or criticize them for having an opinion that they don't agree with. Not everyone is going to be in love with a book, and some loud, opinionated people are going to express their dislike in their own ways and in their own space. Authors need to get over it.
Negative reviews are necessary to sustain a rich, interesting, HONEST literary culture. If we're all rainbows and sugar-puffs because we're scared of hurting some author's feelings, we're doing the book world at large a disservice. If a book is full of suck, say so. You can even say so with snark. You can even say so with ALL CAPS and LOTS OF RAGE that you wasted your money on something you want to rip up and use as paper airplanes. Say it with me now, people: A NEGATIVE REVIEW IS NOT NOW, NOR WILL IT EVER BE, BULLYING.
Bullying is the new buzzword that's being used to describe a particular brand of snippy reviewing (or "reacting," if you don't want to call it reviewing). Considering that an author has to go out of their way to find reviews of their work, I don't see how that can be bullying. "I googled myself and clicked through a couple of links and found your post and I can't believe you called my book crap and YOU ARE A BULLY!!!11!!1!" Anyone who has actually been bullied probably will say that they didn't seek it out. Criticism? Not bullying. Being snarky? Not bullying. Telling your friends that you didn't like a book, and explaining why? Not bullying. Posting a reviewer's personal information so that other people can harass her? Bullying.
And then we come to the "be nice" thing. I've heard a lot of this since this Goodreads thing went up- maybe the reviewers don't exactly DESERVE what's happening to them, but can't reviewers just BE NICE and PROFESSIONAL and POLITE in their reviews, even if they're critical? Sure. But they are under no obligation to do so. They are no one's employee, and are beholden to no author or publisher. We can all pontificate about how reviewing SHOULD be done, but at the end of the day, a Goodreads user's space or a person's blog is his or her own to say whatever. Free speech and all that. And when authors start getting into the habit of blah blah blahing on someone's review, reviewers are going to be less and less willing to be honest.
Of course, it's a free country and authors CAN do whatever the hellz they want. But when an author attacks a paying customer and that paying customer tells people about it and other paying customers stop buying the book or get enraged that a producer of a product is coming down on consumers of the product...those are called CONSEQUENCES.
I guess what I'm saying is that a reviewer/reader/blogger should be free to say whatever snarky/critical/negative thing about a book without having to fear that the author is going to post pictures of a dead bunny in a soup pot in response.
ETA: I absolutely DO think authors should respond to professional reviewers because, after all, who doesn't love a good author-critic throwdown? I'd love to see some literary lawlessness between Michiko Kakutani and Jeffrey Eugenides. Or something.