First of all, the Southern Baptist Convention (i.e., the national denominational apparatus of employees) has no business whatsoever lecturing any church about what it gives or doesn't give to missions. We believe in and practice the association of autonomous local churches. It is not only the privilege, it is the responsibility of each local church to determine and submit to God's priorities for the spending of God's money. I am therefore opposed to efforts to set litmus tests for denominational service based upon arbitrary percentages given through the Cooperative Program. If an autonomous church gives $10 through the Cooperative Program, the Southern Baptist Convention's only suitable response to that is to say "Thank you."
All that just to say that there's no political football here. I've voted for and supported a lot of pastors as SBC officers and leaders whose leadership was exhibited in areas other than their CP giving.
However, as a thinking exercise and not a political exercise, I want to consider this idea that missionaries spend dollars and not percentages, and therefore that it doesn't much matter what percentage a church gives through the Cooperative Program so long as it gives a large number of dollars. On the surface, it sounds like a good idea, but I think that the present demographics of our convention's life suggest otherwise.
People cite a plateauing or even decline of Southern Baptists statistics. These figures seem to suggest a stasis in Southern Baptist life, but that is misleading. I suggest that Southern Baptists are on the move, and in a radical way. Americans are moving rapidly out of rural areas and into the cities. Commensurately, Southern Baptists are migrating out of small rural churches and into urban (generally larger) churches. Thus, although the average SBC church is small, the average SBC person goes to a much larger church than the "average church" figures would lead one to believe.
So, you've got people who grew up in a small SBC church that gave 15% through the Cooperative Program. They move off from that small country church and wind up at a metropolitan church that gives 2% through the Cooperative Program. Let's say, for a hypothetical point of comparison, that 20 such churches are entirely emptied out into a single metropolitan church.
That metropolitan church, although it only gives 2% through the Cooperative Program, is actually giving a much higher dollar amount (by an order of magnitude!) than were any of those smaller churches. But that's not a fair point of comparison. The dollars given to missions by the metropolitan church must be compared to the dollars given by the association of churches that has been eviscerated by the American move from the country into the city. At that point, it becomes clear that percentages ultimately add up to dollars (or else we'd all set them really high).
This blog post does not provide an answer to the question, but it does show how the answer can be calculated. The dollar amount most important to the calculation is the per capita dollar amount given through the Cooperative Program for any given church. I'm willing to suggest that some of our larger churches do pretty well in this regard. At the heart of the question, as it deals with changing circumstances in the SBC, is the simple matter of how many members of the large, urban church that gives a small percentage through the Cooperative Program are people who (hypothetically) could not have been reached by a church giving a higher percentage to missions. Certainly, if we are dealing with transfers rather than new converts, every person who moved from a smaller, higher-CP-percentage church to a larger, lower-CP-percentage church has contributed to a larger number of dollars going to missions from that particular church, but to an overall missions-giving decline.
It would be a mistake to throw stones in any direction over these statistics. Megachurch pastors aren't fueling these developments, nor are the pastors of smaller churches. This is a matter of societal demographic trends, and we're all carried along in some ways on the current of them. We would, however, do well to consider that our convention is in the midst of transition from a convention of many small churches to a convention of fewer larger churches (and historically, the church of 200 counts as a "larger church" in the SBC). If the model for larger churches is one of lower percentage giving through the CP, then the Southern Baptist Convention's cooperative enterprises will be forced to learn to get by on much less money.