Well, I don't know that it's merely all ascribing negative traits to a group with whom people disagree.
With racism/other prejudice, in particular, it is somewhat intuitive to see a link with below-average intelligence. Much prejudice is based on ignorance, fear, and unquestioned learned behavior, all of which less-intelligent people would seem to be more susceptible. In other words, more intelligent people would seem more likely to question dogma and better able to reason through answers.
Beyond intuition, there has been at least one study which shows a correlation between low-intelligence and racism:
EDIT: None of this is to say that there are no intelligent racists; simply that there may well be a correlation and acknowledging that possible correlation might be viewed as somewhat intuitive vs. simply a knee-jerk reaction to ascribe negative traits to those one finds disagreeable.
With racism/other prejudice, in particular, it is somewhat intuitive to see a link with below-average intelligence. Much prejudice is based on ignorance, fear, and unquestioned learned behavior, all of which less-intelligent people would seem to be more susceptible. In other words, more intelligent people would seem more likely to question dogma and better able to reason through answers.
Beyond intuition, there has been at least one study which shows a correlation between low-intelligence and racism:
[1] http://www.psychologytoday.com/blog/millennial-media/201304/...
EDIT: None of this is to say that there are no intelligent racists; simply that there may well be a correlation and acknowledging that possible correlation might be viewed as somewhat intuitive vs. simply a knee-jerk reaction to ascribe negative traits to those one finds disagreeable.