My thoughts on religion is that it is something which many who are involved in religion tend to be staunch about. A person's religious beliefs are something he or she takes very seriously. That said, the religion chosen attracted them for a reason (same ideology). Therefore, any religion which speaks against the person's thoughts would not seem right to them.
On the whole, there are not too many things which people can hold tightly to anymore (politics and religion aside). Therefore, people tend to protect the ideas which bring them closer to other groups and separate them at the same time.