What I am trying to get across to you D, is that there are naturally many, many ways of doing things both in the wider world and in the smaller sphere of one nation, or the even smaller sphere of different regions.
People will and always have used whatever is around them to play music, and they will always take up a new technology, a new idea, when it comes along, be it polyphony or an organ. That's how people work. To seek to restrict a nation to one style, that may have been around two hundred years ago but probably wasn't widespread is folly. How far back do you want to go? Banging rocks together? Likewise to restrict the music to a single line is historically wrong in a lot of geographical and social instances if you want to be accurate.
If you just want to sing a single line then go ahead, but leave off telling everyone else your perceived "right" way to do it. It's just your way, because of your own predilections. It's good to have a cause. Serve it better.