<_<... Well I'm not going to rant as long as Lord did, but everything he says is 99% true. Constrictive criticism is a huge part of just making improvements on something. Without that, you wouldn't make it in any kind of professional career. Yes, some people are rude about it, and yes some people have no common scenes to process that what ever they say might be hurtful. But it's the way is it when you post anything on the Internet really..some will like...and some won't.
But like Lord said, try not to take there criticism to hard. Modifying it before actually posting it up on the Internet, or get opinions from close friends before outing something up. Like take me for example...I do have a tendency in telling the truth when critiquing projects in class. And sometimes, I say good things, and then point it the flaws.
Moral of the story, you are going to run into rude critiquing people. It's just how it is really :p