From W3C Wiki
If you see a flaw in an idea, stop and think about another approach, which doesn't have that flaw, and suggest it. Between BlueSky and real construction work there will be plenty of time to attack the idea.
A BlueSky page does not reflect collective wisdom (design patterns, etc), but rather a collective outpouring and exploration of an idea by people who find it appealing.
[Q. hmm... why not criticize? not even constructively?]
[A. because criticism does two things: it introduces new ideas, which tends to amplify brainstorming activity, and it tends (even when constructive) to make people clam up, which in turn tends to dampen brainstorming activity. The damping effect is almost always much stronger than the amplifying effect.]
[So when brainstorming is the goal, criticism is almost always a bad idea. And since stopping to wonder whether it's a bad idea in this particular case will itself inhibit brainstorming, the best rule in a brainstorming session is: no criticism.]