The reviewer is Freeman Dyson a well respected physicist. The relevant quote:

My own prejudice, looking at religion from the inside, leads me to conclude that the good vastly outweighs the evil. In many places in the United States, with widening gaps between rich and poor, churches and synagogues are almost the only institutions that bind people together into communities. In church or in synagogue, people from different walks of life work together in youth groups or adult education groups, making music or teaching children, collecting money for charitable causes, and taking care of each other when sickness or disaster strikes.

(I have highlighted the part that I'm interested in).

Is it true that congregations consist of a cross-section of the community? It is my impression that most are fairly narrow in breadth. Not only are people separated by denomination, but by race and economic status as well. Is this true?

If it is, what does it say about the ability of appeals for social justice to gather a coherent group of participants?