As is typical, I formulated a two hour essay for a 50 minute class session. Thus, I had to jettison ideas left and right to be at all coherent and complete. Here is one idea that got left out.
Community is based around ritual, and ritual is based in meaningful movement–crossing, dancing, running, and so on. The challenge to Protestant (comm)unity is shared, meaningful movement in ritual. Doctrinal statements invite agreement/disagreement, thus inclusion/exclusion; movement invites involvement. On the spectrum of Protestantism, denominations with more ritual movement may have more unity than those based primarily around doctrinal statements. Doctrinal statements are intellectual, analytical; they lend themselves to contemplation in solitude.
Without ritual movement, then, community will form around other spheres that are not intrinsically linked to Protestant faith, spheres such as sports and politics, for example. These spheres create unity in movement, goal, form, and ritual timelessness. They sacrifice the concept of the individual for a shared, communal identity if only for a time.