Of the many films that dramatise the deranged behaviour of celebrity fans, one of the most popular is Der Fan, a German production from 1982 about a teenage girl obsessed with a pop singer. It begins predictably enough – she writes him dozens of letters – but the ending is a little less orthodox. When he doesn’t reply she intercepts him outside one of his gigs, hangs out in his dressing room, has sex with him, kills him with a statue, chops him up and puts the dismembered body parts in a freezer. Unsurprisingly, it has become a cult classic.

Like most works of its genre, Der Fan taps into a stereotype that fans have had to endure since the emergence of popular culture. Characterised as hysterics, fantasists, psychopaths, geeks, misfits or mindless consumers, they are feared either as obsessive loners who spend their lives fretting in their bedrooms (like the protagonists of most fan movies) or as members of a frenzied mob (screaming teenagers at a Harry Styles gig). The word is still associated with “fanatic” in the public consciousness. We assume that anyone with a consuming interest in a celebrity or fictional universe is this way inclined (unless they are a sports fan, in which case their behaviour is likely to be applauded).

Psychological studies of fans tell a very different story from this narrative of folly. While every fandom has its extreme fringes, in the vast majority of cases, being a fan – and particularly being part of a fandom – appears to have a remarkably positive influence on people’s lives. Gayle Stever, who has been studying the psychology of celebrity for more than three decades and has interviewed thousands of fans about their passions, says she has largely found them to be “normal people carrying on normal lives”, who view their relationship with their idol as similar to an important friendship or a special hobby. Throughout the course of her career she has met “maybe 15” fans who were unwell (these include one who used extensive cosmetic surgery to make himself look like Michael Jackson).

It is hardly surprising that fandoms have a normalising effect on behaviour, for they fulfil an ancient human imperative: the need to be part of a group. The groups we belong to – family, friends, neighbours, colleagues – are an essential part of who we are. They give us companionship, purpose and a sense of security, and allow us to do things we wouldn’t do on our own. Fandoms are social groups like any other. They connect us with people who share our interests, and they give us the courage to follow our convictions. It’s safe to be different, weird or nerdy with your fellow fans as you’re all in it together. Studies have found a “psychological dividend” for mental wellbeing and self-esteem among fans of Star Trek, Star Wars, Harry Potter, Sherlock Holmes, Dr Who and One Direction. The fact that many know each other exclusively online doesn’t seem to diminish the strength of their bonds.

Psychologists refer to this group effect as the “social cure”. It is not the only way people benefit from fan culture. For many, their idol becomes a role model, someone they seek to emulate or who represents an attitude or way of being that might previously have seemed closed to them. Often we are drawn to people whose experience or outlook reflects our own. Taylor Swift’s millions of young fans love her for her music but also for her awareness of the things that matter to them, and because her lyrics about heartache and angst mirror their own trauma. They don’t know her, but her songs make it clear that she knows them.

The screenwriter Jane Goldman, whose credits include X-Men: First Class and Kick-Ass, told me about her teenage fascination with Boy George. She was a fan, she said, partly because of his music but also because his androgynous appearance and uniquely flamboyant style made her believe she could achieve something in life other than what was expected of her. “I saw in him this possibility of going out and living slightly outside of what society tells you to do,” she said. “I remember the first time I saw him on Top of the Pops – it was like something clicked. I’ve spoken to a lot of people who have had the same experience. I felt like an outsider, I wasn’t quite sure where I fitted in the world, and then I suddenly had a sense of belonging, like I had found my way.”

Role models are no less powerful if they are fictional. Indeed, fictional heroes come with many advantages. They are readily available (you can always reread that book or rewatch that TV series). They have dependable personalities. And they come with a ready-made network of like-minded enthusiasts. As with real-life idols, fans tend to latch on to fictional characters whose values they admire. Harry Potter is adored by adolescents because he made it acceptable not to fit in, and because of his close circle of loyal friends. Many Star Wars fans find inspiration in the wisdom and ideals of the Jedi, the ancient order of protectors who learned to channel the light side of the Force through meditation and the control of negative emotions. Among Jane Austen fans, Elizabeth Bennet in Pride and Prejudice is a standout model of courage and independent thinking because of how she defied the patriarchal norms of her era.

These dynamics of hope and transformation are hardly ever discussed in the public conversation about fans, yet they are a common thread, whether your interest is celebrities or classic literature, sci-fi or medieval history. Most fans are on a search for meaning, and they are prepared to give a great deal of themselves to find it. To be a fan means many things, but at its heart it is an act of love.

• Fans: A Journey Into the Psychology of Belonging by Michael Bond is published by Picador.

Further reading

Fangirls: Scenes from Modern Music Culture by Hannah Ewen (Quadrille, £14.99)

Real Characters: The psychology of Parasocial Relationships with Media Characters, edited by Karen Shackleford (Fielding, £18.38)

The Psychology of Celebrity by Gayle Stever (Routledge, £12.99)