Protestant: You know, there are a lot of Catholics who are becoming Protestant as well.
Author: How many of those Catholics fully believed and practiced everything that the Church teaches and holds to be true and leave because they think they've found the truth someplace else? Most of those who leave the Catholic Church leave because they disagree with and never practiced the Church's moral teaching, they got mad at a priest or sister, they don't think their is enough fellowship, the parish is not welcoming, etc. It usually has very little to do with finding the truth someplace else. Those profiled in the book were strong in their prior beliefs (some were even vocally anti-Catholic), but upon searching the scriptures and the writings of the early Church fathers followed truth to the Catholic Church.
I have to agree with the author of the book. Here are some of the reasons people have passed on to me about leaving my parishes.
1. Father kept talking about sin
2. Father kept talking about money
3. I don't agree with Father's staffing decisions
4. I don't agree with the Church's teaching on contraception, divorce, same sex marriage, etc.
5. I never hear about Jesus at Mass
6. I don't like the Mass time.
Perhaps you can share some of the reasons you've heard.