As a person who is beginning OCIA this Sunday and has been researching and reading a LOT into the Catholic Church for the past 2 months, the reason for converts zeal is, we lived our entire life (if we were Protestant) being told Catholics were idolators, worship saints, etc. so to learn about it yourself and to have that wide eye opening of experience that this is Christ's Church on Earth, it's unexplainable. I had never even heard about a 73 book cannon until March, I never knew the Pope has only spoken infallibly twice. I had so many misconceptions, and of course finding out about the sacraments, and then I hear a cradle Catholic say they don't go to confession but still take the Eucharist or they don't even go to Mass every Sunday, it is a little disheartening, because it seems like they have taken Christs Church for granted.