“No stupid questions” is something I think is applicable to any attempt at gaining knowledge, insight or perspective. “How big helicopter would you need to hoist an ice cube to the sun to extinguish it?” Though absurd, there might be a disconnect of knowledge, and the question reveals other things which could be explained.
To me, a stupid question would be some kind of rhetoric which doesn’t seek information, but instead attempts to redicule and push own standpoints or beliefs. “Have you gotten over that religious faith yet?” or “Do you realize how dumb your political views are?”. These are examples of ineffective and condescending and will likely just leave the other person with reinforced standpoints in addition to annoyance. I find that to be a stupid approach and thus a stupid question.