Certain forms of mental illness are associated with disordered or illogical thoughts. This can include delusions or maladaptive coping mechanisms. Racism is not based on logic. Every human brain, regardless of race, has the same underlying cognitive/biological system (it's called connectionism). High levels of melanin is what causes some people to have darker skin. It does not influence mental function in any way. So why do some people and groups use superficial differences, such as skin colour, as an excuse to discriminate? The answer to this is different for different individuals.

Downward social comparison refers to a phenonemon whereby comparing yourself to a group that is seen as lower status in some way can boost self-esteem. It's why watching sad films like the Titanic can make people feel happier later. Racism allows someone to conceptualise others as less than so people can feel like they are superior or better off. Perhaps some people with racism lack other more healthy sources of self-esteem. Self-improvement requires work and it can be an unpleasant process to acknowledge one's own faults. People can sometimes look for an excuse to avoid this, especially if they're intellectually or emotionally overwhelmed.

Reearch has shown links between racism and various forms of poor mental health. This includes racism causing poor mental health, and mental health conditions that cause racism e.g., schizophrenia induced halluciations. Some researchers argue that racism is often a result of how people were educated growing up as opposed to mental illness itself. However, I would point out that brainwashing is associated with anger, depression, complex PTSD, and even suicidal thoughts. Facilitating warped logic in one area can normalise it and make it more likely in another area. The emotion of hate is associated with poor emotional well-being in general. This can include posttraumatic stress, suicidal thoughts, depression, and anxiety. Hatred and fear can even cause physical symptoms such as high blood pressure. One could argue that racism is a form of self-harm.

It's easier to trick someone than it is to convince someone that they've been tricked. There's a bias in human psychology called confirmation bias. People will often focus on information that supports and confirms their views and ignore evidence that goes against it. Once a falsehood is planted in someone's mind it can be very difficult to rectify. Many education systems punish people for making mistakes and making mistakes can be embarrassing. Personally, I love making mistakes because I see it as an opportunity to learn and grow. There's also a concept called the Dunn-Kruger effect. People sometimes lack the skills to realise how poor their abilities are in a given area. This can give people a false sense of confidence in their thinking.

Familiarity promotes liking. It's called the mere-exposure effect. The amygdala in your brian is involved in fear. The prefrontal cortex in your brain looks for memories to calm down your amygdala e.g., if you saw a picture of Godzilla you wouldn't be scared because your memories would tell you it's just a picture and that Godzilla is fiction. However, if you don't have previous positive memories (e.g,. if you had never seen a photograph before) it can make it more difficult for your prefrontal cortex to calm down the amygdala.

There are many many many reasons why some people are racist. With this diversity it may not be possible to label racism as a disorder by itself, but perhaps it can be used as a diagnosis symptom of other disorders. Perhaps more specific forms of racism can be considered disorders. Responding to hatred with compassion can be very difficult and counterintuitive. However, I personally think people who are racist are sick and they need help. Countries that take a rehabilitation approach to anti-social behaviours, as opposed to purely criminal ones, have lower rates or recidivism. Regardless of how people feel in relation to moral idealism, this seems to be a more morally pragmatic approach.

This article has focused on the mental health of people who are racist and not on people who have been victims to racism. A good source for more information on mental health and racism can be found here: https://www.mhanational.org/racism-and-mental-health