“One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision”
Bertrand Russell 
Surveys of the psychological literature suggest only a modest correlation between perceived skill level and actual performance. A meta study showed that poor predictions of skill level relative to others was due to poor assessment of their own skill level rather than an underestimation of the skill level of others.
At the high end, the highest performers showed a small tendency to underestimate their relative performance – perhaps because they find it hard to believe anyone could do as badly as some do.
This pattern is repeated in all walks of life, from complete idiots, to university professors (94% of whom thought their work above average).
As an example, consider someone estimating their performance on an English grammar test. To accurately assess whether a sentence you have written is grammatically correct, you must have a good knowledge of the rules of grammar. Someone who does not have a good knowledge of grammar will not only perform poorly on the test, but does not possess the level of skill necessary to assess their own performance.
Unfortunately life is full of incompetents who insist on commenting loudly and confidently on matters that they are not qualified. Those who advocate complimentary medicine, those who deny global warming, and those who think they are better at Tetris on the Gameboy than me, to name but a few, usually lack the skills necessary to critically and accurately evaluate their position.
Unfortunately, a lot of celebrities use their fame to advocate their own misjudged positions. As it is human nature for the masses to put more weight on an argument given by a perceived powerful (influential) person, democracy will always make bad decisions unless the elected politicians actually take advice from experts that is not popular with the masses. However, politicians will go for the vote-winning position over the right decision every time.
If I ruled the world...