Rate each song individually - you can no more make a judgement for "all folk music" as a single entity than you can for "all books", or "all films".

I think you're missing the point of THIS discussion.

The question as I understand it would be ----taken as a whole, what rating would you put on folk?
just as ----taken as a whole, what rating would you put on a site that discusses the Bible...or what rating would you put on a site that discusses Shakspeare, etc...

Other than that, the comment about context is more to the point and question--that being should context influence rating?