The reasons why any young person leaves their home, family and friends to go and fight in a foreign country will always be complex to unravel.

It does seem incomprehensible that someone who has been raised and educated in the UK with no history of violence would be willing to get involved in acts of unspeakable brutality and yet we are told that hundreds have made that choice. There are clearly powerful global forces in play and we need the input from political theory, theology, history, social science and of course psychology to make some sense of it. Yet, as a therapist, I have been trying to understand why some young British Muslims are being drawn to become jihadis within the extreme group Islamic State (IS) and are willing to kill innocent people seemingly without question.

Fundamentalism appeals because it offers certainty and eradicates unbearable feelings of uncertainty and helplessness.

I don't have a lot of knowledge of the individuals involved but I know that these jihadis are young. Teens and early twenties can be a difficult time involving separation from family, a search for identity, which is often accompanied by anxiety. It is a challenge for the healthiest and most secure. If you are psychologically vulnerable and feel an outsider, this period of life can be fraught, full of anger and helplessness and the promise of a 'solution' might be irresistible.

Fundamentalism or black and white thinking of any kind is appealing in that it offers certainty and eradicates unbearable feelings of uncertainty and helplessness. Extremist views have to hold absolute certitude. You don't win mass appeal by saying, 'maybe' but by saying 'I know' this to be true. Fundamentalist beliefs cannot allow for doubt. Modern life is complex and can be psychologically challenging for us all. This seems to be a factor in why the more fundamental wings of all the major religions seem to be winning followers. Certainty is a powerful psychological glue and respect for different perspectives is an enemy of this glue. We have all known moments, especially when having an argument, when we have felt absolutely sure of our beliefs and been reluctant to see that the other person might also be right.

Knowledge of group behavior and cults has a lot of offer in understanding the power and appeal of an organization like IS. On November 18, 1978, in what became known as the Jonestown Massacre, 912 people from the Peoples Temple Agricultural Project led by the Rev. Jim Jones, died from drinking poison, 276 of whom were still children. It is almost impossible to imagine what can make parents persuade their own children to take a drink that will kill them. This is but one example of the power of the cult to persuade people to madness and violence.

A young British Muslim says "To all my brothers living in the west. In the heart you feel depressed. The cure for the depression is jihad".

A cult will offer its members a sense of belonging, purpose and meaning and above all a feeling of superiority. There will be answers to all questions and problems but the price you pay is non-questioning obedience to the higher authority of the cult leadership. This promise is offered in a recent recruitment video for IS called "There is no life without Jihad". A young British sounding Muslim says "To all my brothers living in the west, I know how you feel [from] when I used to live there. In the heart you feel depressed. The cure for the depression is jihad … All my brothers, come to jihad and feel the honour we are feeling, feel the happiness we are feeling."

The target audience and message are clear: become jihadis, feel significant and happy. What is not explicit is how much the prospect of violence is an essential part of the appeal of groups like IS. They offer the antidote to helplessness, the power of life and death. Elias Canetti in 'Crowds and Power' argues that public displays of killing your enemy are displays of power that indicate to the world that the enemy is weak and must die and by contrast we the killers have strength and are alive. This is surely the message in the filmed beheading of western journalists.

I don't think there are any quick answers to what makes a British Jihadist and the great challenge is not to descend into black and white thinking or a 'knee-jerk' reaction. This can be difficult when feeling threatened but is essential if we are to find creative solutions to complex and threatening situations.