As an American citizen with a deep contempt of Nazism and all it stands for, I have to say this: So long either an Antifa or Nazi commits no act in contravention of American law, both are free to peacefully assemble, preach to whomever will listen, and express their views, insofar as they can legally do so.
Honestly, I find both sides worthy of my disdain, but I will defend to the death either side’s right to express their views without violence, as that is their constitutional right and they are legally protected from anyone trying to detain, assault, or otherwise molest them.
When either resorts to violence, they are violators of the law, as they would be using violence to curtail other political views to the benefit of their own.
Further, I dissent with your assertion mere belief in Nazism, being a member of the Alt-Right, and so on makes one a traitor. So long as they do so peacefully, they break no laws. Same goes for Antifa.
When either side resorts to violence, you are breaking the law to violate the civil rights of others to express themselves, no matter how honorable or perverse their views.
THAT is what I consider a traitor.