Well, I can't speak for singing, but there's no doubt that traditional Irish music of the instrumental variety is "simple" in a number of respects. Overwhelmingly, it consists of short, regular phrases and is mostly diatonic. Playing it involves much repetition. As much of it was made up on instruments, it mostly sits very easily on those instruments, so that virtuosity is never required. Untutored payers can play the music very well (as can tutored players, of course). I understand from fiddle players that they rarely, if ever, have to go beyond first position. "Simple" may mean easy to play, therefore an inclusive kind of music. I'd take that as a positive, not an insult. But "simple" doesn't mean the same thing as easy to play well. Getting to play well may mean following a different developmental path for traditional musicians than for classically-trained musicians, but that should not imply a less musicianly path. So, while I agree with the sentiment of what MacColl says, I think I detect just a hint of defensiveness. But then I'm no singer. ;-)