I'll confess that I haven't read all the comments here. There area around nine pages of opinions...all of them noteworthy...so I just read the OP's opening piece and skipped to the last page. Sorry...
Anyhoo, the point of never responding...I'd agree that it isn't written in stone, but one should always take care not to take any hostility out on the author of the review. If it's a personal attack, my opinion would be to let it go. People like that are more than likely to respond with something even more vicious and who needs a flame war? Move on, move on, move on.
If, OTOH, the review contains a nugget or two of helpful critique, then it might be worth saying at the very least "Thank you for that helpful information, it will help me next time around."
In fact, that's what I did. One reviewer on Goodreads liked my novel Lindsay Versus the Marauders, but gave it only three (or 3.5, I forget) because of an infodump (her words) and I could see where she was coming from. She liked the overall pace of the novel and the action scenes (which everyone seemed to like), but had trouble with parts of the narrative. Okay, so I simply said thanks, I'll keep that in mind and do my best the next time around (or words to that effect).
And I meant it. That's the kind of review I can get into and appreciate. Some carp about Goodreads being this or that, but in the end, they're the ones buying the books. And many reviewers are not writers so they may not know how difficult it is to pen a good piece of prose. That's not a knock by any means. It's simply a statement of fact. What they are, are people who know what they like to read and have a pretty decent idea most of the time about how a sentence should flow and how this and that should be all in place. (And yes, I'm still learning the craft, so I make no claims of being the world's greatest author or anything). So to me it's worthwhile to look at the reviews, see what you can learn from them, and try harder the next time out. My two yen for the day and sorry for the long post, but this idea got me thinking about a lot of things...