Aaaaah, the good old "you shouldn't critize if you haven't created anything argument". Easily applied to "you can't criticize music if you haven't recorded an album" and "Why are you criticizing this movie you haven't even filmed a blockbuster".
Commentaries have a valid point, with or without creation.
I think that you are focusing on "rudeness" too much.
This is the internet.
And this is a (mainly) hacker community -who are not known for their politeness-, and good engineering matters for hackers. (as it should)
I think that this is the perfect medium for rudeness.
The whole reason people post their projects here is to get criticism of any kind.
If one is disheartened because of a rude comment, one needs to grow up.
One needs to learn how to deal with comments; learn to decide on which ones to take seriously and which ones to not..
The good thing about the internet is that most of us are anonymous here. So you can not judge my comments based on my identity (or my history, e.g. what i have done). Nor you can punch me in the face for being rude or something. The thing you get in exchange is honesty (hopefully).
This is healthy. Let's embrace it, and keep politeness and politics for face-to-face meetings.
Commentaries have a valid point, with or without creation.