And if the church is so open that there is no difference between belonging and not belonging, then there is no reason for people to commit Sunday mornings to it, never mind their minted-personality-capital. Likewise, if the institution wants that little of me that is distinctive, then the institution itself has little traction as well. So, even if I was inclined to give to the church (for whatever reason) the fact of the matter is, there are other organizations doing the same work and often doing it better.
Factor in the opportunity to give to specific causes and it is not hard to understand why, in a growing world of generosity, people are increasingly less generous to their churches. Why give to a church-based mission that sublimates its commitments when you can give to a secular program that does a more effective job?
This, of course, flies in the face of the widespread conviction that to minister in the name of Jesus is somehow narrow and fundamentalist. But like so many other conversations in the church, we have thrown the proverbial baby Jesus out with the bathwater. There is a difference between being clear that a ministry takes its spiritual grounding seriously and believes it is essential to its ministry and making the aid we offer conditional on the willingness of people to receive aid. Here Jesus' own behavior is instructive: he healed indiscriminately, but he also didn't hesitate to say, "repent."
Bottom line? Until mainline churches recover a commitment to minting their members, giving will continue to decline.