Purpose
This report summarises how clinical psychology and psychiatry generally understand people who believe that killing others is justified, necessary or required because of a religious or ideological cause. It uses plain language where possible and distinguishes extreme beliefs from mental illness.
Believe it or not – Key finding
A belief that killing people is justified by religion does not, by itself, mean that a person is mentally ill.
This is an important distinction. Contemporary psychiatric literature indicates that members of terrorist or extremist groups do not generally have higher rates of mental illness than the general population. Mental illness appears to be more common among some lone-actor extremists, but it still cannot be assumed to be the explanation for their behaviour.
In other words, someone can be psychologically capable of understanding what they are doing, planning it deliberately and believing that it is morally right, while not suffering from a psychiatric disorder.
1. Extreme religious belief is not necessarily psychosis
Psychosis involves a significant loss of contact with reality, such as hallucinations or fixed false beliefs that are not reasonably explained by the person’s cultural or religious background.
For example:
- Extreme ideology: “My religion teaches that these people are enemies of God, so killing them is justified.”
- Possible psychosis: “God is personally speaking to me through my television and has instructed me to kill my neighbour because he is secretly a demon.”
The first statement may represent an extreme ideological or religious belief. The second could indicate a psychiatric disorder, particularly if it occurs alongside other symptoms of psychosis.
A psychiatrist would therefore ask much more than “Does this person have strange beliefs?” They would examine whether the person has lost the ability to distinguish their beliefs from reality and whether there are other symptoms of mental illness. Distinguishing extremist beliefs from symptoms of mental disorder is recognised as an important difficulty in psychiatric assessment.
2. How can an otherwise ordinary person come to accept killing?
Psychology provides several explanations that do not require mental illness.
One is moral disengagement. This is where a person changes the way they think about an action so that something normally considered wrong becomes acceptable.
An ordinary example would be a soldier being trained to think of an enemy as a threat rather than as an individual person with a family and a life.
In extremist thinking, this can become much more extreme:
“They are not innocent people. They are enemies of God.”
Once someone has been placed into an “enemy” category, killing them can become psychologically easier to justify.
3. The importance of an “us versus them” mentality
Extremist movements often create a very strong distinction between “us” and “them”.
The person may increasingly see:
- their own group as good, pure or righteous;
- outsiders as corrupt, dangerous or evil;
- disagreement as evidence of hostility; and
- violence as self-defence or moral duty.
This is something ordinary people can recognise in less extreme forms.
For example, football rivalry can involve “us versus them”, but most people retain the understanding that the opposing team’s supporters are still ordinary human beings.
Extremism can take the same psychological distinction to an entirely different level, where the opposing group is no longer regarded as deserving the same moral consideration.
4. Religion can provide a powerful justification
Religious belief can become particularly powerful when something is regarded as a sacred or absolute value.
If a person believes:
“This is God’s command”,
then ordinary moral reasoning can change.
Instead of asking:
“Is killing this person morally acceptable?”
the person may ask:
“How could I disobey God?”
This can produce a situation where the individual genuinely believes they are doing something morally good, despite the fact that an outside observer sees the behaviour as horrific.
That does not make the behaviour acceptable, nor does it make the belief reasonable. It helps explain how the person can psychologically reconcile their actions with their own sense of morality.
5. Believing something and acting on it are different
Clinical assessment is particularly interested in the difference between extreme beliefs and a pathway towards violence.
A person might say:
“I believe people who oppose my religion are evil.”
That is concerning, but it is different from:
“I have decided to kill someone.”
And that is different again from:
“I have chosen a target, obtained the means to do it and have started preparing.”
Psychiatric risk assessment therefore looks for behavioural evidence of movement towards violence, rather than simply diagnosing someone based on their political or religious beliefs. Contemporary forensic psychiatry specifically emphasises identifying warning behaviours and distinguishing extremist beliefs from an actual pathway towards violence.
6. Mental illness can nevertheless be involved
Some people who commit extremist violence do have mental disorders.
For example, a person could have:
- schizophrenia or another psychotic disorder;
- severe depression;
- a personality disorder;
- substance-use problems;
- significant paranoia;
- or another condition affecting their judgement or behaviour.
However, clinicians should not automatically assume that the mental illness caused the extremism.
The relationship may instead look something like:
Personal grievance + extremist ideology + social reinforcement + psychological vulnerabilities + opportunity + willingness to use violence
rather than simply:
mental illness → terrorism.
Research specifically cautions against looking for a single cause or single psychological profile for radicalisation.
7. The most important clinical distinction
From a clinical perspective, there is a major difference between:
“This person believes something that I consider bizarre, frightening or morally repugnant.”
and
“This person has a psychiatric disorder that is causing them to lose contact with reality.”
Those are not the same thing.
A person can be completely sincere, highly intelligent, psychologically organised and fully aware of their actions, while holding an extraordinarily dangerous ideology.
That is one reason psychiatry does not regard terrorism or religious extremism as a diagnosis in itself.
Conclusion
Clinical psychology and psychiatry would generally view religiously motivated killing as a complex interaction between ideology, psychology, social influences and individual circumstances, rather than automatically as evidence of insanity.
The crucial question is not simply:
“Are their beliefs extreme?”
It is:
“What is driving those beliefs, how firmly are they held, is the person able to distinguish belief from reality, and have they moved from believing violence is justified to actually intending, preparing or attempting to carry it out?”
That distinction is important because a mentally ill person is not necessarily dangerous, and a person who is not mentally ill can nevertheless become extremely dangerous. Contemporary psychiatric literature explicitly warns against confusing mental disorder with extremist ideology and instead emphasises assessing the person’s actual pathway towards violence.