gavra_at_work-
To your first point. I know it’s a chassidish concept. I am pointing out, albeit as a misnaged, that the concept was made up and has no makor in Halacha, because there’s no such thing as a song which is tahor or tamey. If you make up a concept and that concept generates halachos that the gemara didn’t hold of, then your concept is false according to halacha, period.
As for your second point, the opposite is true. There was a pretty common sheilah back in the day even for those who didn’t sing/listen to music, and that is can the tunes from the church be used by chazzanim in davening. If you had seen my previous posts you would see I quoted the MB no less, b’sheim the Bach, that there is no problem. So first of all it was relevant, and not only that it was discussed and they said it was fine!