How does Jared Diamond deem religion for the average Joe in Guns, Germs, and Steel?
I do not see anywhere where Diamond comes right out and says "for the average Joe, religion is..." Instead, we have to sort of infer what he thinks. I believe that Diamond thinks that religion does not do much for the average Joe.
To Diamond (at least in the chapter about "kleptocracy") the major benefits from religion come to the rulers. First, religion can justify taking money from the little people and giving it to the powerful. This clearly helps the rulers more than anyone. Second, it can give people a reason to fight and die for their communities. This mostly helps the rulers as well because they are the ones who can use the armies to get more power.
A third effect of religion, however, can help people as well as rulers. Diamond says that religion helps make people who are not related by blood be able to live together peacefully. This helps the average Joe because it would make his neighbors less likely to, for example, attack him or steal all his property.