The result is what Potok referred to as a "broad-based, right-wing populist rebellion," generally short of violent extremism.
While not necessarily extreme itself, many groups in the overall movement are "shot through with radical ideas, conspiracy theories and racism," Potok said. "Sometimes these attacks do serve as inspiration for other groups and individuals."
One reason anti-government groups are embracing Stack, rather than distancing themselves from his extreme actions, is that he does not seem to be crazy, Potok said. It's a characteristic that troubles forensic pyschiatrist and ABC News consultant Dr. Michael Welner.
"It's easy to get a sense that someone like snaps," Welner told "Good Morning America" today. "But this is the kind of crime that's planned for a long time... I don't find it to be psychotic. That's the problem here. It's rational."
Schulz believes Stack was simply beaten to the point of desperation by the government.
"The government is routinely allegedly violating the Constitution... Then when you call them on it, they ignore you too. That's enough to drive a lot of people together and to start, you know, some kind of movement," he said. "There are people that are out there so frustrated that say 'Hey it's time to lock and load.'"
Schulz compared Stack's attack to McVeigh's Oklahoma City bombing, saying despite the desperation, any violent act is detrimental to the movement.
"Anybody that commits a violent act against the government sets things back," Schulz said. "The government uses that as more reason to further clamp down... Timothy McVeigh set things back. Joe Stamp set things back."
Online, it appears that many people disagree.
"He sacrificed his life to inspire the quest for TRUTH," one Facebook poster said. "He deserves a memorial. A one man uprising... God Bless him."
"This was quite heroic," said a member of Stormfront.org, a white supremacist Web site. "There is a gradual awakening underway."
"This is just the beginning, prepare for battle!" another said.