Keith
It's not as cut and dried as you are trying to make out. Like most words in our vocabulary it has several different but overlapping meanings and different meanings to different communities. That doesn't stop it from being a useful descriptor. I tend to use it in different ways in different communities I visit. In my research I'm largely happy to use the 54 descriptors but if I'm discussing it with most of my mates who I sing with I know they will largely understand the wider world meanings which have much broader descriptors.

As for 'Jingle Bells' I played it at a gig recently, alongside a whole set of folk songs. Jim is not contemplating singing it in a folk club, but in the wider 'folk' community of pubs, social groups, and any other number of gigs we might be attending. Sometimes it is enough to give people what they are familiar with and can join in with. As for it being 'shite' you are in a very small minority, Dick. It probably resonates with the real folk much more than anything you've ever sung.