Simple and plain there are only two things that fit this model: experience or a text (something inside or something outside). So you'll see liberal Christians focus on doing good things. Conservatives focus on being Biblically oriented. Political conservatives argue that logic should drive our politics. Political liberals look to do things that are right, even if it isn't logical. Thus in my class my conservative church history professor sneers at liberals because they do not follow the Scriptures in their study. Liberal politicians argue that conservatives do not care about the poor. Liberal Christians argue that we need to live right. and Rush Limbaugh points out that liberals are idiots. It all makes sense!
I'm not saying that liberals are any better than people like Rush because they're not rude and they want to do good. I wouldn't say that at all. I'm simply trying to point out that people like Rush will never convince a liberal to stop being leftist...the liberals are judging the contest by a different set of rules! Until he understands this, he'll continue to only argue to the choir.
The issue for conversation is learning to see outside our point of view. Where are there differences what are the goals we are pursueing and how are we pursueing them. What are "the other's" goals and how are they pursueing them. When this happens then we'll be able to see change happen!