Of course, some bring it on themselves
One of my students (not a clueless 18 year old, a very successful Army officer in his late 30s) was recently arguing that conservative, evangelical Christianity is the *only* true form of Christianity. Catholics and liberal protestants need not apply.
Likewise, the pro-creationists on the Kansas board of eductaion have had some choice words for Christians (as as they'd say, so-called Christians) who support the teaching of evolution. Again, as far as they are concerned, the very term "Christian" has to imply anti-evolution, they don't identify themselves as "conservative" Christians.