The KKK analogy is much closer than the aforementioned serial killer analogy. The KKK feels they have a "cause" for their violence, and their "cause" is to "cleanse" our country of those who "don't belong" and advance their (warped) interpretation of Christianity. The "cause" for the violence Muslim extremists engage in is to fight against forces which they see as encroaching on their own (warped) interpretation of Islam.

And let me assure you that, while it's certainly nowhere near a majority, there is certainly a very large contingent in "White America" that doesn't directly support or condone what the KKK does, but believes many of the same things, and therefore "looks the other way" when the KKK demonstrates in the center of town, burns a cross, or spray-paints swastikas on the home of a Jewish family. This "silent acceptance" is a result of agreeing with some or all of what the extremists do, but not wanting to go to the same, well, extremes.

Getting back to what Muslims should or shouldn't do about these acts, I'd imagine that it's the same scenario. Nowhere near a majority of Muslims believe in "Death to America," "Death to Israel," etc. But from what I gather, mainstream Muslim opinion is that the Palestinians (and only the Palestinians) belong in Israel, and America should stay out of the Middle East. So, when you average Muslim sees anti-American or anti-Israeli violence on TV, it doesn't disturb them in the same way that violence against their own people does. Certainly, the average Muslim wouldn't personally engage in these extreme terrorist acts, and they wouldn't necessarily associate with anyone who does... But despite their different interpretations, they're still bonded by the same faith, so they have more in common than they do with the American they saw executed on TV. To them, therefore, the anti-American violence is more acceptable on a relative scale, though not acceptable on an absolute scale.