Currently it is because a large part of the Republican party consists of what we call the &quot;religious right&quot;, a group that seeks to make political change based on what they believe to be religious truth, or morality. Ted Cruz was the arbiter of this ideology in the Republican primaries, until he dropped out last week. While this group does not represent the entire party, they are definitely the most vocal, and many liberals conflate that group with the rest of the party as a whole. This belief is not helped by the fact that many &quot;core&quot; republican platforms come from religious conservatives, like outlawing gay marriage and abortion.<p>Many people who belong to the academic community consider these people to be a bunch of uneducated backwater hicks who do not belong in intellectual conversations based on logical thought. So when an intellectual states that they are an evangelical christian, many consider them to be flawed in some capacity, and thus have nothing of substance to contribute.<p>EDIT: to add to that, evangelical christians tend to embrace a literal translation of the bible; in that the world was created in literally seven days, and that every human is descended from Adam and Eve, a story which in its literal translation is of course not supported by science. So when a person who professes to follow science also professes to be a member of this faith, it can seem paradoxical to many.