I agree with this in general. Positivity is much more useful or productive. However, there are scenarios for which constructive criticism is warranted. For example, it is against the guidelines to show the LEGO logo on the project, lest it give the impression the project is an official project. If someone, unaware of that restriction posts a good project, but slaps a LEGO logo on it, I could see it being beneficial to point out to the creator of the project that they might want to edit out the logo or risk having their project deleted. As is also the case of plagiarism, or any number of proposed projects that violate the guidelines. I think many project creators fail to take the time to read guidelines and TOS's. Also, there are certain projects that will not likely get made, such as ideas containing new element molds. Similarly, I think it is justified to warn unwary project creators that this is probably a no go.