I think most people can see that there's a huge gulf between "everything is lawful" and "the government regulates ideas and risks doing so in their favor".
Most people accept that you cannot say "how unfortunate it would be for him if Jack ate seafood tonight" to your Mafia henchmen. Nor can you say "we will storm parliament at dawn using these weapons" if you are part of a plot to replace the state with a capitalist anarchy.
And in the same manner, it seems that there are plenty of laws in place already against saying "if white people are to defend ourselves and survive as a race, our immune system must go to work" in an 8chan manifesto.
But that's different than saying "Jack has betrayed me", "representative democracy is defective and must be replaced by capitalist anarchy" or "the white race is superior; non-whites are traitors and should be dealt with harshly; vote for me".
(Whether a text advocates violence cannot necessarily be reduced to a few words, as I hope my first example demonstrates. The context in which the words are uttered and the interpretation the speaker can reasonably intend are relevant. Fortunately, no legal system has been replaced by a computer program, but are generally interpreted by intelligent human beings.)
Free speech absolutism was never intended by the Voltaire or the American founding fathers - as can be seen by their other actions. It is a recent populist view without warrant of careful analysis. I support free speech; but I do not support free speech absolutism.