Well Early I agree with you on all points except the last (D)which if it were enforced would exclude anyone of limited musical ability from singing.

It takes practice to sing in tune and on key, so if somone is enjoying singing and hits a wrong note now and then or drifts into another tune by mistake then they need support and encouragement to continue and perfect their songs.

How many times have you heard people singing the Navy version of Botany Bay drifting into the tune of The Eton Boat Song?