Southern Poverty Law Center tracks and documents actions of extremist groups that promote hate, dissension and violence in the US. Often the hate stems from framing “other” people as being “less than” or “unequal”, undeserving of equal rights and access to a the same resources that are available to their group. Their extremist view points are documented in writing, publicized events, and open acts of violence. Each group advocates that their view of morality is justified and should stand above other perspectives of the world. In sociology, this is known as ethnocentrism, believing that your group’s values and moral take precedence over others.
See more at the SPLC website on Extremist-Files.