Mentally unbalanced people often look for extremist political and religious ideologies as a way to explain / turn off the voices in their heads. The cult, and these usually are cults, explain to their newbies why their problems are caused by whatever the cult opposes. The newbie finds a home and friends. The cult, which often actively recruits the unbalanced, has new pliable cannon fodder to work with.
Nokolas Cruz was not a member of white supremacist Republic of Florida. Jordan Jereb, a member of the group, concocted the story to get media attention. The story emerged out of alt-right 4chan, which delights in pranking and hoaxing mainstream media. In addition, law enforcement said they found no links between Cruz and ROF.
However, classmates of Cruz and his own online postings indicate he was racist. So, he got his views from somewhere and was pretty clearly seeking out those with similar extremist views. The internet makes this easy to do and also makes it easy for a lunatic fringe to recruit. This must always be opposed.
Seven classmates of Cruz told The Daily Beast he expressed extreme political views and disturbing behavior when he attended the high school he is now accused of attacking with a high-powered rifle.
“He would always talk about how he felt whites were a bit higher than everyone,” Charo said. “He’d be like, ‘My people are over here industrializing the world and starting new things, while your people [meaning blacks and Latinos] are just taking up space.’”
The prescient Lunatic Fringe, from 1981