Hi Spektical,
Let me take a stab at this.
The question is still unaswered....why do religious people take some stories literally and some not? What makes them so sure about their decision? and if these stories are open to interpretation because of individuality, then why universalize them into beliefs?
1. Why do religious people take some stories literally and some not?
First there are over 33,000 different religions in the world.
A religion is a social institution that includes a set of common beliefs and practices generally held by a group of people
Religion - Wikipedia
That means there are a lot of people with different ideas.
Most have preconceived ideas about what they believe and therefore when they read a story they interpret it in the way that it supports what they believe. So if a literal rendering fits their belief that is what it is. If a non literal rendering fits their belief that is what it is.
2. What makes them so sure about their decision?
Because it is what they want to believe. Therefore it is correct.
3. if these stories are open to interpretation because of individuality,
All stories are open to individual interpretation.
4. then why universalize them into beliefs?
Because without beliefs their can be no religion.
"John 5:39 (KJS) Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me."