And the decline has more to do with less time for Community then anything to do with Religion for we also see drops in other COMMUNAL activities, be in Volunteers in Volunteer Fire Departments to membership in bowling leagues.
In many ways the increase in Religious membership in the 1940s, 1950s, 1960s and even the 1970s reflected that people had more time for their Community and one way to do that was to join a church. We see a similar drop in Church Membership in the period from the late 1800s to the Great Depression, and apparently for the same reason, people did not have the free time or money to be a member of such community groups.
Remember the key to membership in most organization is that the members can be off work at the same time. The need for sleep to make sure you can go to work and do work is almost as important. When it comes to personal relationships, the more one see and interact with one's spouse the better off is that relationship. Thus these three activities are more important then anything else. The problem is more and more employment is off regular hours AND more and more families have both parents work, often on different schedules. Thus between work, sleep and the need to interact with your spouse, all on different schedules leaves less time for activities that are community based (Such as being a member of a Church, Volunteer Fire Department or even a Bowling league) and thus a drop in the number of people in all types of communal activities (individual and to a lesser degree Family activities are holding their own, but it is the communal activities that has seen the largest drop off in people).
Sorry, every time I hear of the drop off in Church Attendance and hear someone cheer about it, I see someone who does NOT understand WHY it is occurring and why it is BAD. It is NOT occurring do to any drop off in belief, but do to people having less time for communal activities. In turn the reason for the drop off in Activities is the drop in income and job security, one can NOT risk volunteering for to many things for you may have to drop it, in any conflict with employment (or your spouses employment). That is the big push since 1980 and that is the same year Reagan was elected and his decision to weaken the Unions by breaking PATCO. Yes, Union membership is also down, and often for the same reason, lack of pay and lack of Job Security.
Thus do NOT celebrate this drop in Church Membership, it is a sign of less sense of Community and with that decline in a sense of Community, less time for things that help each other and the community as a whole.