I won't give FALSE praise- I won't say that it's a wonderful choice of colors if it isn't, or things that are outright lies. If I think the project is awful, I won't comment on it. But most of the time, I can say something truthful about it- like "that is a pattern I want to try."
BUT, there is a time a place for correction, and believe me, it's only with a "friend" that is really close. I have a friend like that- we can each banter back and forth about the mistakes, color choices, etc, but I would be totally heartbroken if a total stranger tried to do it to me!!!
So, remember that, Quilt Police- if you are not that person's friend first, you have NO PLACE to be the one to offer that correction, unless the person placed the question that they know they are doing something wrong and are specifically asking the community for help.