I believe that the "unearned emotion" factor that Peter describes is what gives sickening songs their repulsive aura. There is a genuineness to a song which actually penetrates the cage. It is there because the writer walked the walk and is writing from some kind of personal knowledge. That said, even the most genuine song can be trashed by a performer who is unable to understand it or reconstruct a genuine voice to sing it.
One of my best tips when I was a young sprat was that I should sing songs as though I were in them. On-site.
The first time I heard "The Rose" (Some say looooove...) it was being song by a seventeen year old suburban girl at a talent contest and I would have barfed if there had been a place to do it.
I heard it again ten years later as part of a wedding I was conducting, a friend of the bride singing it a capella and realized it was not such a bad song, kind of sweet and appropriate.
I sang itmyself two weeks ago at a large dinner party, and it knocked 'em dead, if I say so myself -- the point being that it has the potential of being a fine song, but it has to be sung with a sense of genuine experience
This lack of reality, talking something you have never walked, is what annoyed me about the pretty singers dureing the early folk scare of the 60's -- PP&M and the Kingston Trio. It's not that they all had to go shoot someone in order to sing 'Tom Dooley'. But they ought to sing it with a genuine sense of the moment, not as a polished barbershop bit! :>) Frank Warner, on the other hand, sounded as though he'd done it himself, as well as surviving every Civil War battle ever fought single-handed!