The problem is that the Bible isn't necessarily a straightforward book. Some things it comes right out and says, but other things it leaves open to interpretation. In theory this is a good thing for a religion to do, it allows a person to take what they will from a given text, and apply it best to their life. But unfortunately people are weak, and often uneducated. They aren't able to understand the language of the bible, or to fully take it all in. So they rely on trusted teachers to interpret it for them. The problem with this is that often times, rather than getting their own unique interpretation of how the religion can affect their life, they get a rehearsed and manufactured version of their Pastor or Priest's interpretation instead.

Another problem is that in today's world, religion is more like an heirloom than something somebody researches and decides is best for him or her. If it was good enough for the parents, its good enough for the child, and silly religious beliefs are passed down through the generations like eye colors and genetic diseases.