"but if it's a cosy folky-fantasy of working-class life then it's a different matter."
You have no evidence whatever that Blackleg Miner is a "folky-fantasy of working-class life" and what on earth is 'cosy' about it. If Bert took it from The Yahi Miners, as is quite possible with his track record, then it comes with a folk pedigree; if he wrote it (which has never stopped you from including it under 'folk' in the past), he made an excellent job of capturing the bitterness of a strike.
Wherever it came from it has served the revival pretty well since the earliest days of 'Come All You Bold Miners' - therefore, if you are not in the process of disappearing up your own arse, it is a folk song by your own standards (whatever I might think).
You are now in the process of re-writing your own crap definition to suit your personal likes and dislikes and adapting even the re-write as you go along to try to score points.
The fact that you appear to dislike the song doesn't mean squat; it reflects perfectly my own impressions of the atmosphere engendered by a strike. I worked on the Liverpool docks not long after they stopped being casual labour based and the fight for union recognition was at its height, and later when containerisation was introduced, which eventually destroyed shipping on the Mersey altogether, so I saw the effects up close.
God knows, we had enough examples of miner versus miner in the last two strikes to realise to what lengths men will go when their livelihood is threatened. It seems you have painted yourself into a corner - get used to the view.
Jim Carroll