HiI don't think most traditional folk songs have a left political slant, though it's probably true to say that many modern singers interpret them this way. I've always been quite interested in the fact that all the old versions of "The Greenland Whale Fisheries" have the lines
The losing of that whale boys, it hurt the captain sore/but the losing of his men, it hurt him ten times more
whereas almost all modern singers sing it as
The losing of our men, it hurt the captain sore/but the losing of the whale, boys, it hurt him ten times more
Probably says more about the people singing the songs than about the songs.
Seems to me there's a whole lot of songs that are essentially politically conservative. Depends whether and how you sing them, though.
Cheers!
IanC