When you are young and trying to find your way, you are impressionable. I think certain people can pick up on that and take advantage of it. At least this group/cult didn't end in a mass murder/ suicide, as so many others have.
Being impressionable should be based on your level of exposure. I think overly protected individuals can fall for these cults the moment they are exposed to them because they're just that naive. Of course a few illegal drugs here and there during the process makes the transition easier.