Are Republican voters stupid or brainwashed (vote now)?

In his book "What's the Matter With Kansas?" Thomas Frank explores why so many people in the South and Midwest vote against their own interests by voting Republican. What are the reasons for this?  

Racism has been a recruitment tool for the Republican party since the Civil Rights Act of 1964 and has resulted in the entire realignment of the South as a Republican stronghold. However, in addition to this blatant appeal to the darker nature of voters, Republicans, with the collaboration of corporate media, have been remarkably successful in convincing poor and middle-class voters to vote against fiscal, healthcare and educational policies that would be to their benefit. Instead, a large portion of voters, elect Republicans who lower their take home income, reduce their ability to get healthcare, poison the environment and make access to education even more difficult. And, they do this while passing huge tax cuts to the very, very richest individuals and corporations. (more below the fold)

Furthermore, in a poll released today by Gallup, a majority of Americans rejected the concept of evolution and the science behind it while expressing a belief in the literal interpretation of the Bible. Science and scientific methods, it seems, are not to be trusted by a majority of the American people. Can we be surprised that in a nation that rejects logic and critical thinking we have gone from Thomas Jefferson to George W. Bush?

So, the question is:

Are Republican voters stupid or brainwashed?