The problem with using only books to try and understand what people who are disagree with you think is that they aren't interactive. While reading something you disagree with, you will probably find yourself thinking "Well, what about X", and if the book doesn't explicitly address that issue you will never know what they would respond. Even worse, people tend to assume that those who disagree with them don't have an answer to their objections, rather than that the book simply doesn't address them. If you are instead talking to a (reasonably knowledgeable) person, they will be able to at least give some sort of answer to your objections.