The argument that one need not have an electrical degree to turn on a light switch is meaningless. Having been an electrician, I can do all my own electrical work. I don't have to call someone to do it for me. Same with my car. No, you don't have to be a mechanic to drive a car but it sure is nice to fix your car's problems yourself for next to nothing instead of paying $200 to some guy to replace a couple of bushings that cost $1.75 at Murray's. It's nice that if I write a song, I can jot it down myself without needing someone to do it for me.

As for folk music coming more from the heart, I think that's more myth than truth. I recently found a sheet music version of "Where Did You Sleep Last Night" that has a very nice guitar solo that I have since lifted for my own version. I've done the song for years per Lead Belly but this solo really fleshes it out tremendously. I couldn't have learned it by ear. No way I would have figured it all out. But having the music in front of me, I got it down. I learned to play blues the same way--looking at sheet music in books.

I don't know why anyone would argue that it's not a required ability. You're always a better musician for knowing it--always.