This was not a very well argued book. In any serious book, you expect conclusions to be based on real research. Here it was not unusual for the author to support a conclusion based on a few conversations with some friends. Though there was some real research, the continued use of anecdotal evidence made it difficult to trust anything.
Another way the author lost credibility was by taking a position as an insider of a church when in fact there have been recent years of complete absence of from church life. Added to this problem was the uncritical support of nearly anyone who is able to find a way to justify absence from church life.
In case you are wondering, it is church leadership that is nearly always the reason that people leave a church. The possibility that people leave the church because they might be selfish, uncommitted, or immature believers is not carefully considered. Self-reporting of those who leave a church is not always a reliable method of determining the real reason they are leaving.
The book at least brings up the idea of analyzing why people leave a church. Church leadership would do well to continually evaluate why people leave a church and consider how to improve their structure to better keep members. People who leave can often offer valuable feedback to church leaders.