I guess the best thing to do is to make your desires known. If you want CC, ask for it with an open mind and a willingness to accept it good or bad.
Too many times I see someone asking for it then, to me, they get defensive when someone critiques their work. In my thinking, if you don't want to hear it, don't ask. I don't give my "opinion" to open a debate on the correctness of it. If I'm alone in my opinion, disregard it. If it becomes a theme, accept it and move on.
On the other hand, if someone posts a shot and doesn't state that they are just sharing an experience with snapshots (which, BTW, I really enjoy), I assume they don't mind CC.
If that's wrong, I can stop doing it but, personally, I don't really see the point of posting images if it's not to learn from those with more experience/knowledge or to get opinions from less experienced photographers who often see something quite helpful.
If it's just to pat each other on the back with a big "atta' boy!", how do we learn and improve?
Of course, you don't have to be harsh about it either.
As Dimitri mentions, the problem of those seeking just CC without giving it or even seeking CC then never replying afterwards, is a real problem. Then again, it doesn't take long to figure out who those people are and, like him, avoid their posts altogether.
Last thought: I realize that it can be a blow to hear negative comments about an image that you personally feel is quite good. I've had that happen several times but learned from the experience. When I look at those same images now, I can easily see all of the flaws and have a "Why did I think this was great?" moment.
