Via BoingBoing:

"Unlike the "modern math" theorists, who believe that mathematics is a creation of man and thus arbitrary and relative, A Beka Book teaches that the laws of mathematics are a creation of God and thus absolute....A Beka Book provides attractive, legible, and workable traditional mathematics texts that are not burdened with modern theories such as set theory." — ABeka.com

A Beka is a textbook company that services the fundie education market. And they dislike set theory. The BoingBoing post goes into just what it is about set theory that pisses the fundie set off, and it is both interesting and horrifying.