From the Ars Technica article, reading from the judgement, the money quote:
As Justice Kennedy stated for the Court in Ashcroft v. Free Speech Coalition, 535 U.S. 234 (2002), “[t]he government may not prohibit speech because it increases the chance an unlawful act will be committed ‘at some indefinite future time.’” Id. at 253 (quoting Hess v. Indiana, 414 U.S. 105, 108 (1973) (per curiam)). Rather, under Brandenburg, the State may regulate protected expression based on the belief that it will cause violence only if the expression is directed to inciting or producing imminent lawless action, and is likely to incite or produce such action. Brandenburg, 395 U.S. at 447; see also, Free Speech Coalition, 535 U.S. at 253.