Sometimes the truth hurts, but I agree one hundred percent with you. This is an art sharing website, after all. As long as the comment is constructive and I can take something from it, I don't care how well you do (or don't) sugarcoat it. I think it's fair to say a lot of us here on dA are here to improve, anyway. Noobs be noobin'.
Sometimes I wonder if a lot of the people who get really upset about criticism are even ready to be posting their work at all. Sometimes, I wonder if that's hurting them as a writer.
When I started writing, I never showed my work to anyone. I'm so glad I didn't have unlimited access to internet then, or else I may have been pretty upset by any constructive criticism. I'm thankful that I took time to somewhat develop myself as a writer before I started looking to others for advice. Even when I did start posting at the beginning of high school, I'll admit that feedback pointing out flaws hurt me. At least by then I had some level of maturity not to get angry and put my own feelings about someone's feedback in perspective. Most importantly, I had already decided I enjoyed writing and had developed some area of confidence in it. Those who are just getting started and putting their very first pieces up for critique probably don't have either yet, so feedback becomes the motivator rather than developing as a writer.
You're right - we're in a public forum here. Everything we post to dA is going to be for others to see. There are tons of things I've written that I would never let anyone see. Either those things are crap and I've abandoned them for whatever reason, or they are so personal that there is no point in opening them up to criticism.
Unfortunately, a lot of people are posting what I'm guessing falls into one of the categories above. They also aren't expecting criticism to begin with, and they haven't developed the maturity to handle feedback better.
I actually rarely get really critical criticism. I love constructive criticism when I get it. I love to hear it because learning from what I did wrong and improving upon it makes me a better writer! Getting those ones that are only one line long saying things like 'OMG so cool' don't help aside from that brief shot in the arm of a warm and tingly feeling. They let me show people are reading, but is it really going to help me get better? Probably not.
Nobody's out to get me because nobody's out to get me. In the six years that I have been writing, I haven't had any real major complaints in the way I've been writing my recent stories. In my opinion, the characters are believable, have flaws, some of them major as of late, and a world that responds to their actions.
I just don't get reviews as often as I would like. I don't try to include a lot of gimmicks. I just want to tell a story about otherwise normal people in abnormal situations.
Reviews aren't lifeblood, but damned if they don't help!