And then they answer the question, frequently with a no. This usually leads to another argument between those who point out that critics cannot be stopped from saying anything they like about anything they like, and those who think this statement means encouragement of harsh and unconstructive comments. You can get yourself into the damndest positions, defending free speech. Anyway, 'this kind of thing' is really two different things. There is a considerable difference between criticizing something and reviewing it.
Criticism is for the writer, reviews are for the readers.
That's why reviews can be a lot more cruel. The reviewer is commenting on the finished work, telling people what it's like and whether it is, in her opinion, worth reading. Serious criticism of a story, on the other hand, frequently involves discussing how the story works and why, and what might have made it better. The writer of criticism knows that if she doesn't express herself with a certain degree of politeness and consideration of the writer's feelings, the writer won't listen to a word she's saying, in which case the effort she's putting into criticizing the writer's work is wasted. Reviews do belong in public, of course, since they're intended to be useful to other readers, which they won't be if they sit unread on the reviewer's hard drive.