A stupid question, a really stupid question, is one you don't want to know the answer to. To ask about something because you don't know, or don't understand, shows ignorance, not stupidity. To ask about something when the answer is before you and you would be expected to have seen it, shows distraction, and possibly lack of intelligence, but usually it isn’t the result of genuine stupidity. To ask about something you would be expected to know or understand as a part of your basic education or attention to life may attract comment, but if you are trying to correct that deficiency it is not stupid to ask.
No, the really stupid question is the one that thinks it is a triumphant critique, which expects no answer and believes none to exist, but is based on an ignorance and lack of understanding which it explicitly refuses to recognize or correct.
The canonical example, or at least a good example, is 'If we're descended from apes, how come there are still apes?' This is not a stupid question if you are confused by the apparent ambiguity of the terminology and are looking for an explanation. It is a stupid question if you imagine it will overturn, of itself, nearly 200 years of work on evolution.
Talking of which, I’m reading Darwin’s ‘Voyage of the Beagle’. It is absolutely fascinating, an adventure story full of cowboys, Indians, wild animals, sea monsters, bloodthirsty rebel leaders, lands that can kill you without warning with water, drought, mud, rocks, fire or ice, and all of it accompanied by an indefatigable thirst for biological, geological and sociological observation and experiment. He asks questions about everything, and he finds the answers. He never stops. I imagine there must have been a few conversations along the lines of: CD, 'What's that curious creature with a red crest, webed feet and the essential morphology of the Passerine order?' Passing Gaucho, 'It's a... "biiird".'
Every insect, every bird, every reptile and mammal, every river, every aspect of the geology of the area he sees is identified, described, its habits and type noted in detail, every curious or unknown aspect of its behaviour is the subject of experiments, local people are consulted on it for any further information they might have, samples are sent to experts in England for their comments. It is an amazing story of a small part of an amazing life.