Thanks Breezy for the plug...whether one can write a song by committee or not depends I think on the genre and type of song. Pop music, or songs meant to be performed by bands, lend themselves to the committee style of songwriting. While a lot of the mainstream folk (trad and contemp alike) tend to be easier for a single singwriter.

Of course, one can pick up a song and change it later, The folk process works along those lines, and as a rule improves the songs in doing so.

Perhaps the key is in the type of song. Pop/rock puts a lot of emphasis on clever rhyme, what I would call the "outer dressing" of a song. Folk has a lot of "story telling" songs, like ballads. And let's face it - a story is best told by a single person; though someone who hears it may alter it in the telling later.