Post-Modernism

I recently joined a Christian Forum site and one of my posts was on a thread about secular music. There was a girl who started a thread asking people's opinions about listening to secular music. I was quite concerned by the types of responses I heard. It wasn't necessarily what they said, but the kind of thinking that led to their responses. It was very "post-modern." All these Christians were totally throwing off any sense of absolutes, basically saying, "Go with your heart. Whatever feels right." Let me quote one of the responses:

I hate focusing on right and wrong. Let's focus on our hearts. Focusing on what is good and bad, is a trap. What does it do to your heart? Thats the fundamental question. Just ask yourself that. What's right for you, may not be right for me, what's right for me, may not be right for you.

This sounds more like a quote out of a Post-Modernism 101 textbook (they don't actually have textbooks, that goes against their philosophy. Defining themselves would actually defeat the purpose of their philosophy. They're more like a non-philosophy or a non-culture).
Am I the only one who is concerned by this type of thinking? Is our heart really the "fundamental question"? BTW, I don't actually completely disagree with his conclusion, I am more concerned about how he got there.
It got me thinking though. Are our hearts really "the fundamental thing"? Is it always right to "go with what your heart tells you"? What about when our hearts are conflicted? I know I'm not always sure what my heart is saying. How should I make decisions then? It seems to me that we need something more concrete, something more objective to lean upon than the inclinations of our hearts. But that's very un-post-modern of me.