1. If that is in fact what their goal is, where's the threat, since they have zero chance of succeeding?
2. Again, I don't see much significance in focusing upon their purported religious motivations, as opposed to their strategies and tactics.
3. They may use religious messages to recruit and retain membership, but the reality-based "threats" attributed to them don't derive from anything remotely religious.
4. They're nothing more than a loosely-based network of political operatives seeking to advance a socio-political agenda. Nothing new there
1. How did you compute those odds of success? Even a failed attempt can be pretty awful. Like say, 9/11 attacks.
2. You answer your own question quite effectively in #3.
4. You are imposing you sensibilities on them rather than listening to the people themselves.
al-Qa'ida (The Base)
Islamic Army for the Liberation of the Holy Places
World Islamic Front for Jihad Against Jews and Crusaders
Islamic Salvation Foundation
Usama bin Laden Network
Al-Qa'ida is multi-national, with members from numerous countries and with a worldwide presence. Senior leaders in the organization are also senior leaders in other terrorist organizations, including those designated by the Department of State as foreign terrorist organizations, such as the Egyptian al-Gama'at al-Islamiyya and the Egyptian al-Jihad. Al-Qa'ida seeks a global radicalization of existing Islamic groups and the creation of radical Islamic groups where none exist.
Al-Qa'ida supports Muslim fighters in Afghanistan, Bosnia, Chechnya, Tajikistan, Somalia, Yemen, and Kosovo. It also trains members of terrorist organizations from such diverse countries as the Philippines, Algeria, and Eritrea.
Al-Qa'ida's goal is to "unite all Muslims and to establish a government which follows the rule of the Caliphs." Bin Laden has stated that the only way to establish the Caliphate is by force. Al-Qa'ida's goal, therefore, is to overthrow nearly all Muslim governments, which are viewed as corrupt, to drive Western influence from those countries, and eventually to abolish state boundaries.
Established by Usama Bin Ladin in the late 1980s to bring together Arabs who fought in Afghanistan against the Soviet Union. Helped finance, recruit, transport, and train Sunni Islamic extremists for the Afghan resistance. Current goal is to establish a pan-Islamic Caliphate throughout the world by working with allied Islamic extremist groups to overthrow regimes it deems “non-Islamic” and expelling Westerners and non-Muslims from Muslim countries–particularly Saudi Arabia. Issued statement under banner of “the World Islamic Front for Jihad Against the Jews and Crusaders” in February 1998, saying it was the duty of all Muslims to kill US citizens—civilian or military—and their allies everywhere. Merged with Egyptian Islamic Jihad (Al-Jihad) in June 2001. al-Qa'ida (The Base) / World Islamic Front for Jihad Against Jews and Crusaders / Usama bin Laden
Ideology and Goals
The principal stated aims of al-Qaeda are to drive Americans and American influence out of all Muslim nations, especially Saudi Arabia; destroy Israel; and topple pro-Western dictatorships around the Middle East. Bin Laden has also said that he wishes to unite all Muslims and establish, by force if necessary, an Islamic nation adhering to the rule of the first Caliphs.
According to bin Laden's 1998 fatwa (religious decree), it is the duty of Muslims around the world to wage holy war on the U.S., American citizens, and Jews. Muslims who do not heed this call are declared apostates (people who have forsaken their faith).
Al-Qaeda's ideology, often referred to as "jihadism," is marked by a willingness to kill "apostate" —and Shiite—Muslims and an emphasis on jihad. Although "jihadism" is at odds with nearly all Islamic religious thought, it has its roots in the work of two modern Sunni Islamic thinkers: Mohammad ibn Abd al-Wahhab and Sayyid Qutb.
Al-Wahhab was an 18th-century reformer who claimed that Islam had been corrupted a generation or so after the death of Mohammed. He denounced any theology or customs developed after that as non-Islamic, including more than 1,000 years of religious scholarship. He and his supporters took over what is now Saudi Arabia, where Wahhabism remains the dominant school of religious thought.
Sayyid Qutb, a radical Egyptian scholar of the mid-20th century, declared Western civilization the enemy of Islam, denounced leaders of Muslim nations for not following Islam closely enough, and taught that jihad should be undertaken not just to defend Islam, but to purify it. Al-Qaeda
Main article: Qutbism
The radical Islamist movement in general and al-Qaeda in particular developed during the Islamic revival and Islamist movement of the last three decades of the 20th century along with less extreme movements.
Some have argued that "without the writings" of Islamic author and thinker Sayyid Qutb "al-Qaeda would not have existed." Qutb preached that because of the lack of sharia law the Muslim world was no longer Muslim, having reverted to pre-Islamic ignorance known as jahiliyyah. To restore Islam, a vanguard movement of righteous Muslims was needed to implement Sharia and rid the Muslim world of any non-Muslim influences, such as concepts like socialism or nationalism. Enemies of Islam included "treacherous Orientalists!"  and "world Jewry", who plotted "conspiracies" and "wicked[ly]" opposed Islam.
In the words of Mohammed Jamal Khalia, a close college friend of Osama bin Laden: Islam is different from any other religion; it's a way of life. We [Khalia and bin Laden] were trying to understand what Islam has to say about how we eat, who we marry, how we talk. We read Sayyid Qutb. He was the one who most affected our generation.
Qutb had an even greater influence on Osama bin Laden's mentor and another leading member of al-Qaeda, Ayman al-Zawahiri. Zawahiri's uncle and maternal family patriarch, Mafouz Azzam, was Qutb's student, then protégé, then personal lawyer and finally executor of his estate - one of the last people to see Qutb before his execution. "Young Ayman al-Zawahiri heard again and again from his beloved uncle Mahfouz about the purity of Qutb's character and the torment he had endured in prison." Zawahiri paid homage to Qutb in his work Knights under the Prophet's Banner. 
One of the most powerful effects of Qutb's ideas was the idea that many who said they were Muslims were not, i.e. they were apostates. These included leaders of Muslims countries since they failed to enforce sharia law. Al-Qaeda - Wikipedia, the free encyclopedia