For me, it is not just the message, but how it makes me "feel", or rather how it makes my spirit feel.
There are even Christian songs out there that don't feel good in my spirit, either. For instance, there are artists who sing and record worship songs that don't have the "feel" of worship with it, and I don't like listening to their version of the song.
You see, I have a sensitivity to worship (musically), and I have discovered that not everyone has this. But I don't know how to explain to those who don't what is like and how it affects me. I utilize it when I am worship dancing, my body flows with the worship of the song in expressive ways. I'm not sure how to put into words how I can tell this sensitivity is with my spirit rather than my soul, other than it is something that seems to be sensed more in my gut area than in my brain-chemical area.
There are some secular songs I enjoy, though - like "The Land Down Under" because it's a fun song and I have a liking for Australia or some of Weird Al Yankovic's song parodies. I couldn't take a steady diet of such, but I enjoy listening to them when they are being played.
But for the most part, it is more about what the music does to my spirit.
I've struggled with this for a long time. Breaking away from TV and movies is hard though. Of course, now I'm in a situation where I can't watch these. But I really don't mind, because more and more, even with shows I enjoy, there is just too much filth coming out of them that it's disgusting me. Most of my life I've just spit out the junk for the pleasure of what else the show had to offer (like spitting out seeds from a watermelon). But more and more the filth has just gotten worse. I've been asking myself if the pleasure is worth the junk. And unlike the watermelon seeds, the memories don't leave my memory. So I'm stuck with the junk I've watched.
The whole "in the world, not of the world" principle is a crazy line to follow, and it seems we all have different convictions on where to draw the line - and sometimes we focus more on certain aspects than others. I don't know why music gets the bad wrap above TV. But people who are called to minister more to the unsaved an young Christians might be better off having their feet more immersed in the culture of society than those called to worship ministries and the like.
Hope my rambling makes some sense.