Cults live in fear of Grace because it takes away their power. They sell salvation. One of the larger Christian cults tells its members not to listen to any Christian music (besides their's) because it pushes the doctrine of a believer's direct line to God.
Umm - since no one asked yet - whom are you speaking of? Just curious.
FWIW, I've also known people that have been in YWAM and didn't hear of anything out of the ordinary (most of the "spiritual abuse" was coming from outside forces - i.e. witch doctors and such). That doesn't mean that it doesn't happen - just that my friends didn't run into it.