In fact, the majority of Muslims and their clerics are as opposed to extremist acts as anyone else.
According to a Gallup poll taken in England in early 2002, 80% of British muslims would night fight for their country. 49% would fight for Osama bin Laden.

According to another, 77% of muslims saw the military action in Afghanistan as morally unjustified--but 67% saw the Sept. 11 attacks as morally justified.

In another (although admittedly biased), 91% of muslims said they "supported and rejoiced" the Sept. 11 attacks. 89% said that we deserve it because we are an infidel country that supports Jews. 94% said that the attackers died as shaheed (martyrs), and 88% said they supported more attacks.

According to muslim propoganda source Al-Jazeera, 54% of their readers believed that Hezbollah should not be considered a terrorist organization.

According to MuslimUnited, 82% of their members believed that the Taliban should not hand over Mullar Omar.

And according to another poll; 58% of Indonesians, 55% of Jordanians, 49% of Moroccans, 45% of Pakistanis, and 71% of palestinians believed that Bin Laden could be trusted to "do the right thing regarding world affairs." Arafat polled slightly worse, with 68% in Indonesia, 43% in Morocco, 42% in Pakistan, 69% in palestine, and 32% in Turkey.

Likewise, 93% of Moroccans, 91% of Jordanians, 82% of Lebanese, Turkish, and Indonesians, 81% of Pakistanis, and 74% of palestinians were disappointed that Sodom's forces didn't put up more of a fight.

While the 20-30% of more than a billion who don't support terrorism are still a whole lot of people, and the smaller percentage who are actually opposed to it still represent millions, the majority of muslims and their clerics are not opposed to "extremist" (i.e., terrorist) acts.