When people criticism their own or other questions as dumb it's often because there is already an answer they don't yet know, that comes out of their contextual ignorance. More rarely, people fear a question is not smart when it is poorly framed or timed.
Certainly, not all questions are equal. Some are better stated, timed and received. This is not a call for better question filtering since when it comes to questions and ideas, quantity leads to quality: more leads to better.