@layman,
layman: "As I recall, after 9/11, a large majority of muslims said they approved of the attack, and regarded it as just retribution."
Donald Trump claimed to recall something similar. There doesn't seem to be any evidence of it.
Well of course its unfair and discriminatory to suspect Muslims at large, just as it would be unfair and discriminatory to suspect Blacks in general for the crimes of Black criminals, or Hispanics, or for that matter Whites. Is suspicion of criminal behavior that is predicted merely on religion or race something which you advocate?
layman: "Over the years, more and more muslims "claim" they condemn the violence, but you never hear of them reporting suspicious behavior."
How would you hear of it? Do they call law enforcement, or do they call the newspaper? I've seen numerous FBI personnel say, on news shows and in attributed news articles, that Muslims are one of their best sources of information. I never hear of Blacks reporting suspicious behaviour about Blacks, but it seems likely that most police tips and complaints about, say, the activities of the Crips and the Bloods, comes from Black members of the communities where they are perhaps most overtly active.
Sharia law doesn't require death for apostates. The Koranic instruction is permissive, not mandatory. There are many Islamic countries that consider themselves to be guided by Sharia law that do not execute apostates. Like Judaism, modern versions of Islam are not practiced as literally prescribed, by most practitioners. Leviticus 20:13 calls for death to male homosexuals. And there are far more brutal and less discriminating acts and commandments to be found in the Old Testament. Whole cities of unbelievers, down to suckling infants, are put to death. That doesn't represent modern Judaism.
I don't think that in the United States most Muslims would hesitate to drop a dime on Muslim terrorists.
layman: "The problem of course is the "see no evil, hear no evil" posture taken by muslims who are in contact with the perpetrators."
Who specifically are you talking about? Please give me an example where a Muslim had foreknowledge of a criminal conspiracy but, without being a party to it, failed to report it, simply because the conspirators were Muslim.