In the Great Criticism Debate, I've seen a lot of people say they no longer offer unsolicited detailed feedback, because no matter how politely they phrased their comments, the author took offense and hated them forevermore. It's yet to happen to me, but I've also been careful about the authors I respond to. Some stories seem whacked in terms of characterization or plot and usually I just refrain from commenting at all. That seems just as bad as being rude about my reaction. Sometimes silence isn't golden. It just means that an author can't grow into new skills and artistry.