I once spoke with someone about this who took a philosophical standpoint: these cults serve a purpose for some, everyone in the world looks for answers to hidden questions about their existance. A cult provides the answers the easy way. Although I consider this type of thing highly immoral - it does serve a need that the followers have.
But one someone joins a group like this, they end up placeing their trust and their life in the hands of their leaders. The worst of them kill their followers off, or attract government attention. In any case they replace the individuals familly and friends, with they're seductive and highly developed programes.
Praying won't help, since God permits this type of behavior. (He allows a great number of things to occur in the world in the name of free will.)
If you love and care about this familly member, you have a choice. Either honer his ignorant, uninformed commitment to this cult, or take him back by whatever means necessary. I doubt highly that the cult would take legal action, since the last thing they need is that type of scrutiny of their activities.
