Delusions can become perniciously contagious when more than one person not in treatment associate together and enable one another, especially if they are away from outside contact.
About nineteen years ago, I attempted to take care of a man who was in a dangerous manic phase. This man was physically assaultive, was wild, and was harmful to people in the community. When medicated, which was always by force, he was a decent man who wanted to help other people.
(Trying to take care of someone like this is pure folly, and my situation with this man didn't have a good outcome. A few years later, after I was no longer in contact with this person, I was told he had died.)
However, when in treatment, persons with mental illness are often helpful to each other.
"Milieu Therapy" is time spent within a group of people with mental illness--and some psychiatrists believe it is therapeutic. In all fairness, milieu therapy can sometimes be helpful. It allows mental health consumers to commiserate and to not feel as isolated.
On the other hand, when numbers of people with mental illness are put in the same place, sometimes there are common core beliefs and attitudes that get propagated. Additionally, people's delusions can spread from person to person, creating a collective set of delusions.
For example, an idea was circulated that was called, "spiritual warfare." This apparently consisted of an imagined battle of good versus evil, and the battle takes place on a "spiritual plane." Thus while "spiritual warfare" to my understanding doesn't usually involve anything physical, it can make people act in ways that are very unusual.
If someone with psychotic tendencies would like to get well, it is probably a good idea to be exposed to some mainstream belief systems. If all of one's contacts with people consist of being around other mentally ill people and mental health caregivers, it prevents a person from being exposed to a "normal" version of reality. In that case, one learns how to behave like other mentally ill people, but one never learns how to exist among anyone else.
The environment in the mental health treatment system can help, or in some instances, can keep a person stuck in a less conscious, less aware state. It seems that people with mental illness have created our own subculture.
People with a later onset of their illness have had more of a chance to develop normally in their lives. Not all of those with a severe mental illness have always been immersed in institutional situations. In my life among other persons with mental illness, I have met numerous people who have been more successful than I, who have lived more normally. I have met others who are more impaired than I.
The more time spent among others with mental illness, the more someone will be mentally offset from the mainstream. This can interfere with having a significant recovery.
Doing some kind of meaningful activity within the community, such as a volunteer job, can help improve one's condition. Going to school is another option, if one doesn't feel ready to go into a job. There are also online resources that can give people remote contact with others, which is less immediate but better than nothing.
Spending all of one's time around others with mental illness may be unhealthy. However, for a limited time, involvement in the mental health treatment system can often help.