The speech the plaintiffs said was improperly restricted:

1. “train[ing] members of [the] PKK on how to use humanitarian and international law to peacefully resolve disputes”;
2. “engag[ing] in political advocacy on behalf of Kurds who live in Turkey”;
3. “teach[ing] PKK members how to petition various representative bodies such as the United Nations for relief”;
4. “[E]ngag[ing] in political advocacy on behalf of Tamils who live in Sri Lanka.”

The Court’s holding: The statute, as interpreted by the Court, is not unconstitutionally vague, does not violate the plaintiffs’ freedom of speech, and does not violate the plaintiffs’ freedom of expressive association.

This is one of the few cases where the Supreme Court simply felt that a compelling state interest exists which supercedes the First Amendment, so the government is allowed to regulate these activities.

I'm not sure why we have any policy interest in preventing Americans from advocating non-violent conflict resolution with terrorists. Both the decision and the dissent here speak to that policy issue.

Its certainly a thought provoking case.

The Volokh Conspiracy » Holder v. Humanitarian Law Project