Richard Spencer isn't a nazi. before he was sucker-punched on video, he literally said neo-Nazi's hate him. He has never advocated violence against anyone, nor is there any record of him using violence against anyone. He simply wants to establish a white nation to protect a small section of the white race from demographic replacement.
He is a white nationalist and white identitarian, but not a white supremacist, and definitely not a neo-nazi. He doesn't want white people to disappear from the earth, partly becasue he doesn't want any race to disappear from the earth and partly because he is himself white so he is focusing on whites rather than some other race. He believes that the races are different, not superior or inferior, just different, and he thinks those differences are valuable and should be preserved. He doesn't want a race war, he doesn't want to exterminate anyone, and he doesn't advocate for violence.
Even if he was a nazi, if he hasn't harmed anyone or called for anyone to be harmed, you don't get to use violence against him.