First of all, I'm not sure who the "they" is that you're talking about. In any case, neither the violent jihadists (al Qaeda) or the nonviolent stealth jihadists (Muslim Brotherhood) would leave us alone. Of course not. They won't leave us alone until they achieve their goal of worldwide caliphate.
"The process of settlement [of Islam in the United States] is a "Civilization-Jihadist" process with all that the word means. The Ikhwan [Muslim Brotherhood in North America] must understand that all their work in America is a kind of grand jihad in eliminating and destroying the Western civilization from within and "sabotaging" their miserable house by their hands, and the hands of the believers so that it is eliminated, and Allah's religion is made victorious over all religions."
Mohamed Akram,
"An Explanatory Memorandum on the General Strategic Goal for the Group in North America" May 22, 1991, Government Exhibit 003-0085, United States vs. Holy Land Foundation, et al
And the words of Osama bin Laden ? >>> In an al Qaeda training manual, bin Laden attributed the loss of the caliphate to a malaise in the Muslim world.
"The bitter situation that the nation has reached is a result of its divergence from Allah's course and his righteous law for all places and times. That [situation] came about as a result of its children's love for the world, their loathing of death, and their abandonment of jihad." (al Qaeda training manual,
http://www.fas.org/irp/world/para/laden.htm.)
Bin Laden, in his "State of Jihad" speech on Al-Jazeera also said: "The Umma and its youth, women, elderly, must offer themselves, their expertise, and all sort of financial support enough to raise jihad in the battlefields of jihad. Jihad today is a duty of every Muslim."