As a fanartist and writer that I am, I believe critique is always good and positive for growth.
However, I do believe that we must remark a few things. Let me divide them into "critique is..." and "critique is NOT..."
Pointing out both good things/bad things about the art/writing.
A thoughtful comment addressed for improvement, not detriment.
Thought carefully before sent/posted.
Extensive and often helpful.
Contains suggestions for correcting flaws.
Sincere and done in good faith, either for good or bad.
Pointing an artwork/writing flaws with real proof and with precision.
Is done regardless personal tastes/dislikes/beliefs/prejudices/etc. *
* Does not apply when it comes to ilegal or unethical things like pedophilia, plagiarism, art theft, etc.
Critique is NOT...
A comment where you show yourself as a jackass
Neither 100% prais