"There is a feeling that some injustice was committed against you," Waller said.

Those issues aren't new. What's different now is "increasing tribalism," a prevalence of guns in the United States and a feeling, encouraged even by our nation's president, that it's OK to lash out at people who are different from us, Iden and Richardson said.

"People fear mental illness because they don't understand it," O'Connor said. "Fear leads to hate. Hate leads to suffering."

Limiting access to guns among people who shouldn't have them and learning about mental illness through programs such as Mental Health First Aid are parts of the solution, advocates said.

One thing people would learn is that many people they know live with a mental illness.

O'Connor, for example, lives with major depressive disorder and generalized anxiety disorder and is a suicide attempt survivor.

"My experiences with mental illness have made me more compassionate and more likely to protect people than hurt anyone," O'Connor said. "I live a satisfying life and can use my experiences to help other people."