What do people mean exactly when they accuse someone else of not thinking/deciding for themselves?

In another thread, @dutchbrossis said:

“I don’t let a [pre written] book tell me what is right and wrong, I decide that for myself.”

I hear these sort of things all the time from non-believers as well as people trying to give advice to others about not succumbing to peer pressure. While I understand the sentiment of not being lazy about the task of reasoning.. I fear that there is some laziness in the formation of these opinions and I would like to investigate it a bit further.

What I don’t understand is how anyone sees a significant difference between “deciding for yourself” and “deciding for yourself” after consulting a muse, such as a holy book written years ago or the style or behavior of your peers.

Aren’t people still deciding for themselves regardless of whom or what they consult for guidance? In the case of religion, it’s not as though religionists ever do everything in the holy books according to just anyone’s interpretation. They all seem to reason on what ideas are and aren’t important within those holy books to follow and they do only those things that pass a reasonableness test of some sort by the individual.

I find it very difficult to view this behavior as being any stranger than consulting the weather channel before leaving the house, reading up on the latest Dawkins book before going to a religious debate, or asking a shoe-store clerk for advice on where to find a rare style of boot.

Questions on my mind
1) I want to know.. what are people really trying to say in such cases (as i quoted above)
2) What is meant by the concept of “Not thinking for yourself” ?
3) Is it possible that this is ultimately an oversimplified and unrealistic accusation against someone else? (ps. i think it is!)