Apply Bayes theorem. P(you don't find a good argument among stupid people | there is a good argument) is high. P(you don't find a good argument when you've made a true effort to scour high and low | there is one) is lower. Obviously the existence or otherwise of a good argument is only indirect information about the truth, but it still helps.

That it seems there are no two people who cannot disagree without both having the strong feeling that their argument was clearly the stronger must of course be borne in mind when weighing this evidence, but it's evidence all the same.