1) No! As long as people want to write songs for fun and others want to sing them, they will survive up there with the commercial songs. There is nothing special about commercially written songs that give them the power to erase other songs. I agree with Joe - very few songs, outside of advertising jingles, are written purely to make money.

2) Sports fans taking up a commercially popular song to sing on football terraces doesn't automatically make it a folk song but it can happen. It may stick around for a season or two and then fade away or like "You'll Never Walk Alone" it can become engrained in the nation's consciousness to the point where even non-sports fans associate it more with football, and Liverpool F.C. in particular, than with the musical Carousel. At this point it has taken on a life of its own and is a good candidate for being described as a folk song.

DC