THE PROBLEM OF HATING SPEECH Kevin Drum sums up the problem of hate speech laws: "I'm not convinced that content-based speech restrictions can be defined in a broad enough way to make them workable but a narrow enough way to keep them from being dangerous."
In the case of Britain and its terrorism promoters, I'm somewhat ambivalent. I'm certainly against deporting citizens of the US for advocating terrorism (though I have no problem with stripping citizenship from dual-nationality American citizens who have clearly indicated their allegiance to a foriegn power; until the 1960's, you couldn't have dual citizenship in America, and I'm not so sure that was a bad thing). But what about immigrants? All but the very hardest-core open borders folks would allow that we, the current citizens of the United States, have a right to some say over who gets to come join us in our reindeer games. And advocating the killing of our civilians would seem to be a slam dunk disqualifier.
As I understand it, a major reason that Britain has heretofore not shipped its firebreathing troublemakers abroad long before is that they are signatories to the EU's declaration of human rights, which forbids them from deporting anyone to a country where they will be killed or abused. Sidestepping the thorny debate about whether a country should hold itself morally obligated to support refugees because of the bad behaviour of another state (many refugees end up in Europe's generous welfare systems), it seems hard to argue that you have a moral obligation to worry more about the impending mortality of people who are encouraging terrorist attacks than about the well-being of the citizenry they are attempting to decimate.
I suspect that if terrorist attacks continue, Muslim immigration to Europe and America will be slowed to a trickle, or even reversed in the European states where decades of guest-worker imports have combined with stringent citizenship requirements to produce a hereditary alien class. This may, of course, be what Al Qaeda wants; the fewer Muslims have intercourse with the West, the easier it will be to stir up hatred against us.
Update Eugene Volokh has more. His post points out that the above usage of "immigrants" is incorrect, since what I mean is "non-citizens". Naturalised citizens should, and do, have the same rights as born-and-bred ones, with a few limited exceptions.