I have personally observed this kind of group in martial arts, actor/clown collectives, medievalists, student politics (a long time ago), and a couple of religious/pseudo-religious organisations. This does not mean that all groups for martial arts, acting/clowning, medieval re-enactment, student politics, and even pseudo-religious/pseudo-scientific businesses ARE cults. But they are kinds of organisations where I would keep my eyes open.
Some useful and informative web pages to check out are:
Combatting Cult Mind Control by Steve Hassan. Also, more Internet-specific material may be found at the Cults on the Internet (Memetics related page) site. Also a bibliography of Memetics papers on the web many related to cults is here. Isaac Bonewits wrote an Evaluation Framework for assessing a potential cult. It is included here (and may be freely distributed, if accompanied by Bonewits' copyright notice).
Cults may or may not do damage and fraud outside their group. They are likely to disrupt the families and social circles of cult members - increasing distance to strengthen boundaries. They may propagate all manner of nonsense and distorted beliefs. They are likely to make outsiders feel uncomfortable, unless recruitment is on the agenda - what might you have that they want?
The boundaries between the group and the rest of a social structure are characterised by carefully established belief systems. These belief systems are normal contrived and re-inforced by the leader(s) and stake-holders of the group - those with something to gain by manipulating their flock. Sometimes, the belief systems emerge spontaneously - but their persistence is absolutely encouraged by those who benefit thereby.
The leader(s) also enforces a set of behaviours which add meaning to the boundaries. This includes restrictions on: 'who you talk to (openly)', 'who you listen to', 'covert vandalism and sabotage', and recruitment strategies - all under the badge of loyalty .
Typical manipulation, by those in power, use the underlying phobias of the susceptible individuals who join the group. IE, whatever makes them wince (self-image concerns, 'moral outrage', identification with a shaky ediface, etc) are used to re-inforce the phobia and control the 'mark'. Often, the leader leads the flock to believe that external factors are threats and competitors for prized resources or scarce opportunities. The leader establishes: a value system, a social hierarchy, and information distortion.
Phobia manipulation to stop members from leaving (or even talking to outsiders in depth) is very common and extreme - 'they can't be trusted', 'our aims will be contaminated', 'the world will end', ...
Much research in recent years - under the broad term Memetics has focussed on the establishment and stability of various types of cults. On the whole, the movement of the cult is power based and linked to a distorted set of beliefs. The leader often has schizoid tendencies.
A dichotomy exists between those inadvertent cults which form, and those which are directed and manipulated. Historical evidence indicates that both kinds of cult are intrinsically stable - one might even say stuck .
A person with a good self-concept and an interest in truth (and a healthy sense of doubt) is far less vulnerable to cults. However, nearly anyone can be vulnerable at the 'right' time - when lost or disillusioned or feeling rebelious.
Tom Osborn - 1997, edited 2001, 2005.