Critiques are very uncomfortable, that's why I usually don't ask for one, not sure if I can handle it.
I do agree with your stamp, because critiques are very separate from regular comments and it is the artist who encourages people to critique their work. If they don't want their work to be constructively criticized in anyway they have the option of leaving regular comments open.
Several people mentioned this before, and that is having a balance of positives and negatives of the work. So the artist has something they can feel good about and something they could focus on.