The document (the PDF is here), one of the CIA's Red Cell Special Memorandums, is titled "What If Foreigners See the United States as an 'Exporter of Terrorism'?" It outlines how various terrorist groups are taking more advantage of America's openness and multiculturalism to recruit our citizens for foreign operations — something that's much easier now, what with the Internet and social media. Then it looks at how, if this idea of America as an "exporter of terrorism" were to become a more popular narrative, foreign governments may be less willing to cooperate with the CIA and other U.S. intelligence officials.
In other words, if American citizens are joining terrorist causes in countries around the world, governments of those countries may have some questions!
• Foreign regimes could request information on US citizens they deem to be terrorists or terrorist supporters, or even request the rendition of US citizens. US failure to cooperate could result in those governments refusing to allow the US to extract terrorist suspects from their soil, straining alliances and bilateral relations.
• In extreme cases, US refusal to cooperate with foreign government requests for extradition might lead some governments to consider secretly extracting US citizens suspected of foreign terrorism from US soil. Foreign intelligence operations on US soil to neutralize or even assassinate individuals in the US deemed to be a threat are not without precedent. Before the US entered World War II, British intelligence carried out information operations against prominent US citizens deemed to be isolationists or sympathetic to the Nazis. Some historians who have examined relevant archives even suspect that British intelligence officers assassinated Nazi agents on US soil. (S//NF)
So the lesson of this Wikileaks-provided memo: the British Army is coming. No? Then this: It's that we should keep a lid on our crazy citizens joining foreign terrorist operations, because then foreign countries might not let the CIA kidnap and indefinitely detain arbitrary terrorist-looking people from their sidewalks anymore.
Update: Just to clarify: a "Red Cell" paper like this doesn't signal any shift in policy or, necessarily, any extreme concern within the CIA. They're research papers, or, as Wired's Spencer Ackerman writes, "mundane thought experiments." So it's unclear why Wikileaks' Julian Assange plucked these few pages for release to the public, beyond pointing out the not-so-revelatory idea that "hypocritical America produces terrorists too!"