No Right Turn suggests that calls to exterminate those who insult Islam "are little different to those expressed by pro-death penalty protestors, or those who think that all homosexuals should be killed." But - to paraphrase Sesame Street - one of these calls is not like the other ones. Can you guess which one?
Pro-death penalty protesters are advocating for institutional change. That makes it fundamentally different in kind from the other examples. Islamists have the political right to advocate that we institute capital blasphemy laws, and homophobes are allowed to ask that we institute similar penalties for being gay. (They rest of us may then respond by telling them where they can shove it.) But free-speech moderates can consistently grant all this whilst holding that "vigilante" threats or calls for extra-legal violence (whether against cartoonists, gays, or criminals) should not be permitted.
NRT says that "you cannot (consistently) insist that people have the right to insult and offend Muslims, but that the latter are not allowed to be insulting and offensive in return."
This is deceptive rhetoric. It elides the significant differences between the kind of 'offenses' found on either side. No sane secularist would deny the Muslim's right to draw and print rude cartoons about blasphemers and infidels. What some deny is that they have the right to threaten to kill us. (Spot the difference?) This is a perfectly consistent position (so long as they likewise hold that westerners may not threaten to kill Muslims, of course).
In fact, I tentatively support this moderate free-speech position. I think that death threats should probably be illegal, even generalized ones such as those discussed here. Don't get me wrong: people have the right to advocate any institutional change, no matter how wrongheaded we believe it to be. Our commitment to procedural liberalism requires this much. But when advocacy goes beyond the legal framework, inciting violence without respect for the liberal political process, then their speech has gone beyond its liberally protected grounds. There's nothing there worth protecting. If you call for murder, you're a criminal yourself, and should be treated accordingly.