Dimwitted suburban fucktards like Jace generally latch on to extreme racist right-wingnuttery for pretty much the same reason 13 year old boys become juggalos, listen to death metal or go to comic book pics - because it gives them the sense of power and control they crave but do not (and in Jace's case at least, cannot) have in real life. Neo-nazi racism has a certain shock value that Jace, Tyce and Eli (the Three Stooges of bigotry) find useful with which to intimidate other neighborhood kids, toddlers, their grannies, etc.
tl;dr - They're bigots because they want to be ruff-tuff badasses instead of the wimpy little wet farts they really are.