Anything that gets this issue into the media is a good thing, and if writing letters complaining about this helps keep it there, more strength to your writing arm. But genuine indignation seems inappropriate here - unless you think that anyone making equivalent throwaway cracks about Morris Dancers or Bodhran players should be keelhauled. That would thin down the ranks of folkies in England very considerably.
While we're complaining, maybe a few complaints might be in order about that weird piece by the "Times Arts Correspondent" posted above by The Shambles. Aside from the errors Malcolm pointed out, they couldn't even get right the central issue here: "It is a criminal offence for more than two to play together in pubs and restaurants".
Which is nonsense. The offence is to allow that to happen if you are in charge of the premises, if you haven't got a PEL. The musicians aren't breaking any law. (And of course if it's a restaurant without a licence, even a single person playing or singing requires a PEL to be in place.)