The only people I would consider dumb are the people who will not accept fact no matter how much evidence is proven against them or will not even hear someone out on their ideas. If they wish for you to elaborate, well I don't consider that a mark of non-intelligence.
Request for elaboration is one thing, asking for elaboration but then shutting your brain down is one thing.
This all stems from an English lesson once, when our teacher wanted to point us Scotland on a world map. I did this quickly as I'm rather good with geography, but then this one girl experiences a jawdrop and, baffled, asks me how did I know such a thing. HOW COULD I NOT!? She was placing Scotland in South Africa, god damnit! Okay, I start quickly briefing main locations where English is spoken in. Y'know, pointing out where is Canada, India and all that. After my brief speech she still doesn't remember where Scotland is. All this time she focused her entire brain capacity, ALL OF IT, to process the amazing fact that I knew where Scotland is. And this was seventh grade.
That I call ignorance. Or all right, just one branch of it.
Those who refuse evidence and don't listen to opinions I just call mental defects and usually ignore them completely. I keep an open doors policy myself and am ready to give up my own principles if they are proven as fallible.