These guys are religious zealots. That's the root cause. They see Israel and the USA as immoral, decadent societies that have tainted the Middle-East.
From Osama's
Letter to America.
"The creation and continuation of Israel is one of the greatest crimes, and you are the leaders of its criminals. And of course there is no need to explain and prove the degree of American support for Israel. The creation of Israel is a crime which must be erased."
...
"(c) Under your supervision, consent and orders, the governments of our countries which act as your agents, attack us on a daily basis;
(i) These governments
prevent our people from establishing the Islamic Shariah, using violence and lies to do so. "
...
"(Q2) As for the second question that we want to answer: What are we calling you to, and what do we want from you?
(1) The first thing that we are calling you to is Islam.
(a) The religion of the Unification of God; of freedom from associating partners with Him, and rejection of this; of complete love of Him, the Exalted; of
complete submission to His Laws; and of the discarding of all the opinions, orders, theories and religions which contradict with the religion He sent down to His Prophet Muhammad (peace be upon him). "
...
"(2) The second thing we call you to, is to stop your oppression, lies, immorality and debauchery that has spread among you.
(a) We call you to be a people of manners, principles, honour, and purity; to reject the immoral acts of fornication, homosexuality, intoxicants, gambling's, and trading with interest. "
...
"(b) It is saddening to tell you that you are the worst civilization witnessed by the history of mankind:
(i) You are the nation who, rather than ruling by the Shariah of Allah in its Constitution and Laws, choose to invent your own laws as you will and desire. You
separate religion from your policies, contradicting the pure nature which affirms Absolute Authority to the Lord and your Creator. "
...
"(iv) You are a nation that permits acts of immorality, and you consider them to be pillars of personal freedom. You have continued to sink down this abyss from level to level until incest has spread amongst you, in the face of which neither your sense of honour nor your laws object.
Who can forget your President Clinton's immoral acts committed in the official Oval office? After that you did not even bring him to account, other than that he 'made a mistake', after which everything passed with no punishment. Is there a worse kind of event for which your name will go down in history and remembered by nations? "
There you have it. They're like Pat Robertson + Jerry Falwell and ready to kill.
I don't know about you, but I like drinking, gambling, and the separation of church and state. I don't think I should be killed for that.