I can't say that I've seen more than one or two truly mean-spirited critiques here during my (admittedly limited) tenure. I have seen crits that were quite blunt, but only very rarely is it that someone will come along and tell you that you have a big nose and a bad personality, and by the way, your mother dresses you funny. I do a lot of work as a beta reader and critter for writers I've met here, and my style is upfront and blunt. Critique takes a significant amount of time, and I work under the assumption that nobody would ask me to make that sort of time commitment if they did not want to improve their work.
A good critique, of course, is a balanced critique -- it's not just useful to know what you've done wrong, it's useful to know what you've done right. But a thick skin is a valuable thing to have, and as a beta reader, I expect my writers to be able to tell the difference between mean-spiritedness and bluntness. If I see something in your writing that doesn't have the effect you're going for, the kindest thing for a beta to do is to tell you in plain language. Clear communication is a beautiful thing.
If I put my writing out there -- I want reactions from it! And yes, of course I want people to fawn over me and tell me how wonderful I am. But the truth is, occasionally (only very occasionally, mind) I am not actually wonderful. And I want to know this right away, while I can address the issues. It's not enough for me to write. I want to write well. And writing well requires being open to criticism, even though it is occasionally painful, even if it is occasionally unhelpful, even if it is occasionally mean-spirited.