"It seems to me that these adapted spirituals were sung by protestors during marches, during church and community services before the actual protest, and while protestors were in jail to boost their morale, to forge unity, to motivate, encourage, strengthen resolve, provide emotional support, and provide solace to those protestors"
strikes a chord with some research I recall hearing discussed recently and I seem to recall it appearing in a Mudcat thread on whistling.
The singing that Azizi describes is the glue that forms and maintains a community. Many communities over at least the last millenium have been formed and maintained by people singing together and quite a few distinguish themselves from other groups (with whom they share so many similarities that they might all "be" one community) on the basis of what and how they sing together.
Singing by workers at rallies, strikes, pickets etc seems to have always been part of the Australian industrial landscape (and those of most English-speaking countries, I suspect) for a long time but, in recent years, the songs seem largely to have been replaced by chants. On hypothesised reason has been the gradual rise in emphasis on the individual as a singular entity rather than as part of a group. Mudcatters might be a biassed population sample, as many of us get into group singing and other forms of group music but, on a recent visit to Sydney I was fascinated to observe that more than 50% of the people walking through the streets were wearing earphones with mp3 players (mostly iPods) attached.
To me, this seems to be just the extension of music (and thus singing) as 'music for the person' rather than 'music of the people" and it has no 'automatic engagement' component that would stir the listener out of being a passive consumer into becoming an actively contributing participant.