One of the many problems with Christianity, of course, is that Christians can't seem to agree on what Christianity actually is!
Some say it demands the sort of violent, exclusionary treatment mentioned in the article; others say not. No one can "prove" who's right, though, because the Bible itself is so vague and contradictory. It can literally mean almost anything the person reading it chooses to "believe" it says.
This is part of its evil genius!