Ever sat in on a session where there's only super-fast, wall to wall tunes all bloody night? The problem often is that big "instrumental sessions" end up being just that. Anyone wanting to sing is occasionally tolerated if it's a short song, then it's straight back to the playing or more often than not, simply ignored.
I would prefer to hear music and song, but frankly the ego problem exists with the musicians who think they are the only ones who should be allowed to decide what goes on in a session; PP being an example of just that.
Has he never heard a badly played fiddle, or a set of pipes drowning out everything else? Don't think that all the poor quality exists only in singing sessions....

PS I didn't get out of bed on the wrong side today..