We tend to vote for people we see as confident. For maintaining confidence, it seems, ignorance is good and talent is bad.

http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

Quote:

The Dunning–Kruger effect is a cognitive bias in which an unskilled person makes poor decisions and reaches erroneous conclusions, but their incompetence denies them the metacognitive ability to realize their mistakes.[1] The unskilled therefore suffer from illusory superiority, rating their own ability as above average, much higher than it actually is...

Well that explains sarah palin at least.