I wish I could claim credit for this theory, but it comes from Dinesh D’Souza. See Dinesh D’Souza Finds the ‘Common Thread’ in Ferguson and ISIS.
The common thread is the lashing out at innocent people in a misguided attempt to correct perceived injustices. Excerpt:
D’Souza referred to the recent beheading of American journalist James Foley by ISIS. “Behead guys who have nothing to do with it,” he said. “Go and loot shops from business owners who are not part of the original problem whatsoever. And all of this is then licensed by the left and licensed to some degree by the media.”
There must be scores of Americans who want to punish America for something, and those people could probably be easily persuaded to the radical Islamic cause. It's surprising that it hasn't happened already, especially in prisons.