If the Tamil Tigers do it (Holder v. Humanitarian Law Project), then it is soliciting assistance for terrorist acts, but if the KKK does the same thing (Brandenburg v. Ohio) it is protected speech. I really don't know that there is more to say about it then that.
As Justice Potter Stewart said in his concurrence in Jacobellis v. Ohio, "I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that." (that's his complete concurrence)
The same could be true for terrorism. We know it when we see it. No objective definition necessary, so we will make do with it as a political label.
As Justice Potter Stewart said in his concurrence in Jacobellis v. Ohio, "I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that." (that's his complete concurrence)
The same could be true for terrorism. We know it when we see it. No objective definition necessary, so we will make do with it as a political label.