Witnesses to anti-social behavior must speak up to support the lone voices of people who confront it to reduce the risk of such behavior becoming tolerated in society, according to new research. Three studies into the impact of bystander conduct showed that when bystanders step in to support someone who is calling out mistreatment or harmful behavior it sends a strong message to onlookers that this behavior is unacceptable, helping to prevent a gradual erosion of social norms.