Try to be patient with an old man, Brian. The point I was failing to make is that the songs that have come down to us are frequently a long way from the "originals", either by the natural processes of oral transmission, duff transcription, sheer laziness or misconception. The older tonalities are indeed lovely; the perpetuation of frankly eccentric variations brought about by a collector writing down what he heard from an oldster losing the tune is less so. It's a thin line to tread - Beethoven suffered from the reverse of it when copyists altered a crashing discord because "he surely didn't mean that..." Same goes for words that don't make sense. When the song was written, the odds are it would have made perfect sense as the person making the song would have been likely to be involved in the subject or narrative. As to hateful words which "absolutely must go", they are part of the song, and a lesson in how we regarded our fellow man at the time, perhaps even a warning to us now. I would sooner not sing the song than Bowdlerise it or wilfully cause offence. To be honest though, I think it's disrespectful to your audience to sing things you frankly don't understand, especially when you can find out what a doffing mistress did in about five minutes on Google.
I enjoy researching the songs and music (no shit, Sherlock), others have no time for it - it's my passion, but it ain't the end of the world. Mind you, I did draw the line when somebody asked me how I was spelling skillimarinkidoorium...