Wow. However, to be susceptible to brainwashing, the 'victim' has to find something appealing in what they're being told. There has to be some willingness there, a need to believe something different from the 'norm.' Brainwashing is another term for 'convincing.' Convince me what you say is in my best interest, and I'll probably go with you, right? If I can't be convinced, well, you failed
To deprogram someone, you just re-convince them that what they were convinced of is harmful.
Yes, certain environments can certainly aid in the cult's success rates... as with everything. Retailers do it all the time. Make what you're selling appeal, make the atmosphere conducive and appealing, and you'll sell more widgets. Plant the seed in my mind that I want a fresh pretzel, and when I happen upon your cart, well, I'm probably gonna shell out for a fresh pretzel.
As firm as we all like to think we are in our beliefs, the brain is a malleable thing. And if it's not, you have a person who is hard-hearted and stuck in their ways, and in my personal experience, generally unhappy.