I like the episodes other than those that deal with, and there isn't an easy way to say this using words that label, religions that have been around for a LONG time. I have issues calling them cults. Jehovah's Witness would be one. If you look at conversations that identify why some people call them a cult (very strict rules, indoctrinated, etc...) that really applies to ALL religion. Protestant or Catholic Christians indoctrinate their children too, but they would use the word "teach". They ALL have rules, but it's a matter of how much those within the religion follow them. For instance the Bible makes it very clear about what a Christian is (follow the teachings of Christ, teaching the message of Christ), but may if most don't know how serious that is. If they did, they'd be driving around neighborhoods talking to strangers. The difference is in Christianity, many if not most people who CALL themselves Christian don't really live a Christian life (and I don't mean living poor) because the church they go to doesn't make it clear about what BELIEF really means. You can't believe something that is so life encompassing as religion which is teaching you how to live life, but only pay it lip service. It is life engaging.
So, I don't like a series that differentiates what in my mind would be a religion (Jehovah's Witness) because of it longevity and number of members because it's not something like Islam or Christianity. All religions were started by men, and the teachings are based on what the religious leaders believed is correct view of God's message to humans, along with how to life a life. So, a better series would be "religion, cults and extreme beliefs" and then not try to separate them out, and best to show all religions.
I'm non religious, but was brought up in a Christian household, where my Dad was a Dr. of Theology and going to church was mandatory, along with learning about Christ, along with spreading the word of God (Christ = Christianity).
