Vulnerability, I believe that Vulnerability makes one suseptable to brainwashing.....If a person or child is brainwashed.......they had a spot for the cults to get in b/c cults like to prey on people that have some sort of desperate need to be fulfilled......ie, parents, kids, relatives. My parents in particular were vulnerable to it b/c they had a failing marriage and a teen that they did not understand or could not understand at the time, and professionals and friends at the time told them that the program would help all. As for me, I was vulnerable because I had an unhappy family life due to the "failing marriage" and abuse suffered by me at my fathers hands.
I do not believe that these are the only factors that makes one suseptable to mind control techniques though, as these are only a few examples.
warm regards,
-DP