As a celebration of harmony, shape note singing's an ironic thing to argue boat. Still, it's easy for even a casual observer of singings (sangings) to understand why shape note singing fans feel so passionate about it they can't help but battle for it from time to time.
I've done some poking around over the years about Daniel Read, who was born in Attleboro, MA, where I live, and considered one of the foremost American composers of the post-Colonial period. Initially I perceived that, regardless of the unique beauty of his fuguing tunes, his music was, if not dead, at least quarantined to the academic world. Then I spotted his name as the composer of hymns included in the Sacred Harp. Shape note singing has kept Read's work alive all these years, though mostly far from his native New England. Billings has been served in a similar way, and I believe there are others. It also seems to me that Angel Band and Wondrous Love -- and, again, others -- came into the folk music canon via shape note singing.
In my mind, shape note singing has frequently served the cause of artistic justice, preserving the worthy despite the ignorance of others.