Gaiman has talked about this quite well: http://journal.neilgaiman.com/2008/12/why-defend-freedom-of-... The quotable is "The Law is a blunt instrument. It's not a scalpel. It's a club. If there is something you consider indefensible, and there is something you consider defensible, and the same laws can take them both out, you are going to find yourself defending the indefensible."
This precedent stood until Brandenburg v. Ohio when suddenly the Supreme Court reversed itself in order to stop the KKK from being outlawed, deciding that it was now suddenly really important for violent rhetoric to have full First Amendment protection. The KKK was actually much further over the line than the precedent-setting groups - they backed up their talk with a long and bloody history of actual violence and murder against black people. In fact some of the speech that the Supreme Court ruled was protected, such as cross-burning, was actually created as a warning to any black residents that they'd be next if they didn't leave town. Somehow the justices cared more about protecting this than they did about protecting actual, political statements that challenged the status quo.
The Wikipedia entry for cross burning indicates that it has been handled negatively in the last five years–that is, the act of cross burning was not protected as speech–and makes no mention of Brandenburg v. Ohio. That Wikipedia entry does not indicate that cross burning was a significant question at stake in the case, since the matter being decided was the constitutionality of the Ohio statute.
Admittedly, that's just a reading of Wikipedia and I have no training in law of any kind, but it doesn't seem as provocative as you put it.