It's FEAR. Members of abusive groups live under constant fear and are scared to death. Fear is what holds them in the group, whatever "the group" is. "Leaders" instill intense fear in their followers. Leaders of abusive groups indoctrinate and manipulate people to feel fear and helplessness, which in turn engenders dependency upon the leader to make value judgements and to provide a sense of safety. Day to day life such groups is difficult and exceedingly stressful because the members live in constant fear. Fear is the glue that holds them together. It's FEAR, not secrecy. The secrecy is the by-product of the fear.