In a study that screams to be wildly misinterpreted, people subjected to chaotic and disordered environments were shown to be more likely to discriminate against and stereotype others.
The study took place in the Netherlands, and looked at the way people interact with other ethnicities when in situations with high amounts of litter or signs of urban decay — which were helpfully cleaned up in time for the control studies. Researchers also did lab experiments where they asked people about their desire for structure in their lives. When presented with disordered, ordered, and neutral environments, the participants' desire for structure spiked. According to the researchers, stereotyping and discrimination are caused by a mental need to organize and pigeonhole people to try and create order, as it satisfies the desire for structure in the subject's minds.
The obvious implication of this study is that cleaning up urban decay, litter, and graffiti can work to prevent and minimize discrimination in just about any environment.