See, what happens is, that people aren't willing to say openly that they hate another group of people, not even to a anonymous pollster on the phone. The social taboo is just too strong.
Of course, the truth of the matter is that people hate all sorts of other people for all sorts of reasons. Evangelicals weren't willing to say that they wouldn't vote for a Mormon come hell or high water, but as my professors study showed, they weren't willing to vote for a Mormon, and the evidence is fairly clear that it's straight religious bias. You just have to work around what they are willing to openly say and try and get to what they really mean. That's fairly standard political science/public opinion research.