Let's say for discussions' sake that I came to your house, didn't like your decor, and made a point to vocally criticize it in front of other guests. Would you consider that acceptable?
The courtesy not to speak out unbidden regarding someone's work should be given in public forums; don't have something nice to say, don't say it. On the other hand, if the artist asks for critique or makes it otherwise known that critique is welcome, offer it honestly but politely.
Let's say for discussions' sake that I came to your house, didn't like your decor, and made a point to vocally criticize it in front of other guests. Would you consider that acceptable?
The courtesy not to speak out unbidden regarding someone's work should be given in public forums; don't have something nice to say, don't say it. On the other hand, if the artist asks for critique or makes it otherwise known that critique is welcome, offer it honestly but politely.