My experience is that folk singers mostly do know where the song comes from or at least where they think it comes from. Here in the Borders at least tune players tend to be of the two kinds. Some knowing lots about the tunes - others not even remembering what some of the tunes are called never mind where they originated.

I'm talking though not necessarily about folk performers and enthusiasts but about people in general - especially on the likes of youtube etc. And I'v seen also what one poster up the thread describes where it is pointed out that a certain song isn't actually Irish (for instance Dirty Old Town) and the other poster suggests it is just "the English" trying to steal Irish culture. There are clips where, for instance, Luke Kelly introduces the song as being about Salford - but even if you guide people towards that they still won't have it. For some reason some people need these songs to be Irish and get quite agitated when it is suggested that they aren't. It is very strange. As I said there is nothing wrong with knowing where songs come from and in many cases that enhances the song's meaning. And of course it is not just an Irish thing it just seems to more common with them. However I've seen people here convinced that certain songs are definitely Scottish with that being based seemingly solely on them first hearing the song being sung by the Corries or the fact that pipe bands have taken to playing the tune!