Yeah, I tend to think that not responding at all is safer. I'm not in a position to have to worry about this right now, of course!
I know that the times I've seen an author respond to a negative review, the only reply that doesn't make said author look like a tool is to say thank you even if the review is really bad. A couple of times I've seen authors attempt to school their reviewers on how wrong they are, and I just cringe. Especially when the negative review is actually very reasonable/accurate. Most reviewers I've seen get responses like that have just laughed it off, rather than going on the attack, but even in that situation it's done nothing good whatsoever for the author. It just comes off as petty and defensive.
With my 'reader/reviewer' hat on, I can think offhand of two occasions when an author attempted to explain why I was wrong in my review, and on both occasions the reasoning was flawed anyway (though I didn't flip my lid at them because I am, fortunately, not the crazy stalker type



) and, crucially, it made the author look bad/unprofessional. Especially when you've taken the time to say exactly what made you give the bad review (say, the characters didn't engage your interest, or there was too much info dumping and it became boring, or that the author's information on a given subject was inaccurate, etc), having the author come back and say you're wrong, or that you should have kept reading, or whatever, just really doesn't make the author look good.
(My personal favourite was the book I stopped reading mainly because it was dragging on and becoming incredibly dull because it stopped on a regular basis to throw in a huge info dump of not very interesting information, presented poorly. The author told me that I should have kept reading and that the information was necessary...

I (politely, bien sûr!) pointed out that it was his job to keep the reader interested and engaged, not the reader's job to plough through yet another hellishly dull chapter (I was a little nicer than that

) in hopes it would eventually start to improve. Especially given that the book a thriller/suspense novel, not some deep story delving into the human condition. Tolstoy he was not...

)
In the cases where the review is clearly a personal attack rather than an actual review, I think it's even more dangerous. The person who just hates the book isn't likely to change their mind because the author tells them they're wrong, but the person who's fishing for a response is liable to explode all over the place in a rather messy way...
