Adam Ford, a Christian cartoonist, made this comic that I’ve seen several people sharing online:
The full strip is here and you should read the whole thing to understand his perspective.
In short, it acknowledges what the studies have been showing: Christianity is losing people while the “Nones” are growing. But Ford suggests that the shift has everything to do with people who never really cared about religion one way or another — the “cultural” Christians — and simply use whatever label is most convenient at the time.
There’s probably some truth to that. But I think Ford dismisses a very real concern that Christians ought to have: Not everybody leaving the faith is simply apathetic about faith.