There is no "nation of Islam." Islam is far too decentralized for such a concept to exist. The caliphate hasn't existed for hundreds of years, and perhaps never will again. As I've posted before, because of the decentralized nature of Islam (think of how the Church would be if the highest authority was a Bishop, and all wards were run independently), Islam as a religion cannot do something collectively about terrorism. While is is the responsibility of Muslims everywhere to oppose terrorism and extremism, this battle must necessarily be fought in individual mosques and by unofficial Muslim groups (like CAIR). Because there is no unified body of believers, there's nothing to excommunicate an extremist from, and thus there is no concept of excommunication (or anything of the sort) in Islam. Not only is that terribly insensitive, it would do more to promote anti-Americanism and extremism in Islam than a million crazy imams ever could. The Ka'ba or Mecca is not the cause of extremism in Islam: it is ignorance and illiteracy. Think about it: if you were living in Pakistan, couldn't read Arabic, your brother was killed by a drone, and your imam told you that you must fight against those that killed your brother by suicide bombing yourself, what would you think?