I'm really late to this conversation. It was a frequent topic of discussion ages ago. I don't even want to guess how long ago because I'll probably be off, but it always flares back up a bit whenever a new particularly bad incident happens. While I know I've commented on others' posts, retweeted things, etc. about the topic before, I've never discussed it at length.
That's largely because I've never been personally attacked by an author after writing a bad review for one of their books. (Fingers crossed that I didn't just jinx myself with that statement.) I'm particularly happy about that because I review so many self-published books, and that does frequently mean that I've had correspondence with the author. I also think they're generally more likely to find my review even if we haven't been in contact with each other, and they potentially have fewer people advising them against responding to negative reviews (although it should be common sense).
I have, however, had authors respond to negative reviews I've written in a way that wasn't an attack. This has only happen once or twice, and it was so long ago that I can hardly remember the exact details at this point. All I remember is that it felt very awkward because it consisted of them thanking me for writing a review and me struggling with how to respond when we were both very aware that it was a negative review.
Just a general tip for any author: please don't respond to a negative review (whether that be through a comment, tweet, email, or anyway else) even if it's to thank the reviewer for reviewing. Others may disagree with me on this, but it makes me feel awkward and uncomfortable. You know at that point that the author has read what you wrote about their book, and it's impossible to say anything about the review without that hanging between both of you. I think it's just better not to do it.
That is still, of course, nothing like the attacks I've seen authors rage on other bloggers when they are unhappy with the reviews they write. Some of the attacks (or, I feel like I should say, all of the attacks) are rather ridiculous. No matter what you write, someone is going to hate it. Ernest Hemingway is considered one of the best, and I still just barely tolerate most of his work. Don't even get me started on Old Man and the Sea. Clearly, he's a talented writer because so many love his work, but that can't be everyone. That's why it feels so ridiculous when authors attack reviewers.
None of that is even mentioning just how horrible many of these attacks are. I know that the horror stories that stand out in my mind are the outliers. Most authors who respond to negative reviews even aren't as extreme as some of what has happened in the past, but still, it goes without saying that authors shouldn't get up in arms when someone writes a bad review.
That shouldn't need to be said when this topic has been discussed so often, but then again, I never would have thought that it needed to come up in the first place.