I agree. The only music I have had problems with while camping has been electronically amplified. People strumming a guitar and singing is usually fairly quiet and only noticeable when walking close to their site. Anywhere I backpack people are spaced far enough apart to be a non-issue for me. I think if you are close enough that you can hear someone strumming a guitar then you should not be expecting that much solitude.

The only musicians I have had a problem with were at Reyes Creek Campground in Los Padres NF. I didn't realize beforehand the campground bordered a tiny vacation village that was a throw back to the 1920's when it was built. The bar there has a band on Saturday nights and the band parties all night in the campground with people who went to the show. Not a great campground to bring my 2 year old sons to.