This is something I find interesting. AFAIK in the US because of free speech nobody can really do anything in law regarding racism. In the UK in the last few years there have been several high profile cases of racial abuse on Twitter and the racists have gotten jail time (one example at the bottom of the article linked below).
Protecting free speech is important. However most people probably agree there should be a line drawn (for example I doubt anyone would object to a group like the KKK being banned). The problem is enforcing that line fairly and not punishing people for speech that should be allowed is too difficult.
It's an interesting and important problem and becoming more so now that everyone has the means of reaching an audience online.
As a resident of the UK, I think that if we did have a written constitution, regrettably free speech wouldn't be on it. As much as I personally believe in free speech, I do get the impression that the general public here don't.
Which is absolutely fine ― at least then those people wouldn't be able to hypocritically claim free speech as one of their country's positive attributes when trying to distinguish themselves from "barbaric" countries like China or those in the Middle East while also suppressing free speech when it fits their "multicultural" agenda.
Moreover, the UK would then get a lot of shit overseas, particularly in America, for being an example of how European-style socialism leads to a lack of civil liberties, and that might put pressure on the British to actually codify that right.
I had a British lawyer tell me that in no uncertain terms, the UK has a written constitution. It's just not on a single document named "The Constitution", but a collection of documents covering different things.
As for doing things on a whim that violate basic principles of the country, when it comes to constitutionally-mandated protections against unreasonable search and seizure, I'd rather go through UK airport security than US. Then there's oddities like 'free speech zones', where you can say what you like, but only where you're told to. The second amendment is hardly 'clearly codified' - it's highly ambiguous, yet has such significant impact on US society.
The US consitution has some great stuff in it and was a watershed document, but it's not a magical shield simply because it's written down on a document named 'constitution'.
Well, lines have been drawn. "Fighting words", "obscenity", "clear and present danger", "libel", and so on. There are a lot of checks on speech, some of which people feel go too far. And it's the purpose of the courts to set precedent and handle fuzziness.
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."
Disturbingly, when dealing with free speech the US courts are actually more likely to defend the indefensible. For instance, the US Supreme Court unamously ruled that anti-draft speech - actual political speech - wasn't protected by the First Amendment in Schenck v. United States, and the same again with groups advocating Communism in Whitney v. California.
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.
That's completely justified. Although they're obviously both bad, harming the national war effort is far more dangerous than racism against a subgroup of citizens. The number of lynchings of black Americans doesn't even come close to the casualties suffered in WWI.
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.
Another interesting tidbit is that the US does very poorly when considering 'freedom of speech' with respect to the media. In the Press Freedom Index, the US comes in at #47 of 179, as compared to the UK's #28 (and the raw scores aren't in the same neighbourhood either). It's just a reminder that speech in the US isn't as free as it's said to be.