Adding a drumkit, electric guitar, bass, screaming vocal, and other elements of folk rock doesn't invalidate the song. The song remains a folk song. Adding guitar, banjo, bodhran and other "newcomer" instruments, didn't invalidate the song 100 years ago...or whenever. Understandable lyrics have nothing to do with the genre, but how they are sung and/or recorded. There will always be folks who think certain instruments aren't folky enough...but where does one draw the line? Play what you enjoy, rock it up, strip it down, up the tempo or slow it down. Keeping the music alive in any form is much better than to let it die out with old fogeys.