Hate groups are defined by the Southern Poverty Law Center as groups with beliefs or practices that attack or malign an entire class of people.

According to a new study by the SPLC, U.S. hate groups have grown in number by 54 percent since 2000, and in 2008 alone they grew in number by 4 percent.

According to CNN:

Dr. Alvin F. Poussaint, a professor of psychiatry at Harvard Medical School who studied the issue of hate crimes, said people in hate groups can feel paranoid about a specific group of people. This panic leads them to feel threatened, and they may react with violence, he said.

Alternately, individuals in a hate group may sometimes transplant their own personal rage onto a particular group that has no real connection to the cause of that rage, he said.

“Their thinking is very distorted,” Poussaint said.