"But folk could be so much more than just a genre of music (and vastly more popular) were it not for the nefarious influence of it's self-appointed custodians."

These "self-appointed custodians" are, of course, "The Folk Police". People who have the temerity to have opinions on folk music and to express those opinions on forums like this (oh, the evil bastards!!).

These opinionated monsters, by preferring older, traditional forms, and not enthusiastically endorsing the latest fads and fancies, are often seen to be, by implication, 'criticising' other people's tastes in music. This is, of course, anathema to those who either have no opinions of their own or are insecure in their opinions.