'The Vow'

I recently watched a documentary on sky TV called 'The Vow'. An absolutely stunning insight into what it is to be a victim of a 'cult' following, much like the horrific Charles Manson followers. Unlike most shock documentaries, this one described the way people of all backgrounds can fall victim to the theories put forward by hypnotising leaders.  

What struck me was that the most susceptible people are those who go into it with an open mind, something which I believe is  the cornerstone to all scientific thinking. Nothing is ever fully understood, it is only known in layers of complexity. So the question that struck me was that of 'How do you know the difference between scientific knowledge and that with a hidden agenda?', something that effects most parts of modern life in such a  divided world.