> So that blows a hole in the idea that there's no clear line somewhere
https://en.wikipedia.org/wiki/Jacobellis_v._Ohio and https://en.wikipedia.org/wiki/Miller_v._California come to mind. Obviously these involve government censorship but the idea that you "know it when [you] see it" seems to apply for Nazis...
From Jacobellis:
"Stewart wrote, "I shall not today attempt further to define the kinds of material... But I know it when I see it"
From Miller:
> "However, the Court acknowledged "the inherent dangers of undertaking to regulate any form of expression," and said that "State statutes designed to regulate obscene materials must be carefully limited."[12] The Court, in an attempt to set such limits devised a set of three criteria which must be met for a work to be legitimately subject to state regulation:
> whether the average person, applying contemporary "community standards", would find that the work, taken as a whole, appeals to the prurient interest,
> whether the work depicts or describes, in an offensive way, sexual conduct or excretory functions, as specifically defined by applicable state law; and
> whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.[13]
This obscenity test overturns the definition of obscenity set out in the Memoirs decision, which held that "all ideas having even the slightest redeeming social importance . . . have the full protection of the guaranties [of the First Amendment]" and that obscenity was that which was "utterly without redeeming social importance.
I don't think many average people are fooled by groups that try and hide behind the principles of free speech when they walk through the streets chanting slogans associated with the ideology of the Holocaust.