It isn't that ignorant people are "incapable" of recognizing their ignorance. Most people are capable, as you point out, However, most people also exhibit a willful disregard of their ignorance and work diligently to convince others (and delude themselves) they are competent whether or not they really are. In my opinion, that is an intrinsic function of the ego. Everyone wants to believe they are competent, that they have good judgment, and their self-assessment is positive. Nobody wants to believe they are ignorant, even if they are. The desires of the ego are stronger than the desire to have an accurate assessment of your own capabilities. So whether the people are incapable or willfully ignorant is not really important because the effect is the same. People make poor decisions based on flawed thinking, poor reasoning, and a lack of understanding of the underlying issues involved.