As a rule, I do not comment on art or stories that I don't like. Not because of some twisted sense of political correctness, but because I do not think it would help. However I do post critical comments, usually very detailed and explanatory, on works that I liked, but I found lacking in this or that area.
I do believe that even geniuses like Caravaggio or Chateaubriand became who they were through hard work in spite of their natural talents. And I also believe that constant encouragement and criticism allowed them to improve upon the mistakes of their beginnings. When I sense potential in an artist or a writer, I tell him/her what I think they do well and what I think they do wrong, honestly and respectfully, but nonetheless without censoring myself, even though it can be seen to the casual observer as something "not nice to say". They all said, without exception, that it helped them improve... which is why I think none of my comments have been deleted so far 😀