There was a controversy several years ago where at least one Catholic diocese in the US outlawed the singing of "Danny Boy" at funeral masses. The "grounds," I believe, were that the song was "secular" (if not downright "Protestant" -- the melody, after all, is known as "The Londonderry Air," not the "Derry Air.")

Even those who are mightily sick of the song should agree that this was a complete overreaction. If the grieving loved ones want "Danny Boy," their wishes should certainly be respected. (Especially if the dear departed's name was Danny!)

This issue was *probably* discussed in one or more of the many previous threads referenced above.