Terrorism finance is one activity that has profited from the recent economic downturn, according to this article by Dr. Rachel Ehrenfeld. Saudi funding for Hamas, for example, has surged. If there are shortfalls in legal revenues from oil and gas, terrorists can easily replace them with income from various criminal activities such as drug traffickling, arms smuggling, or counterfeiting.
In addtion, sharia finance is making steep inroads into important US financial institutions. The individuals promoting sharia finance don't hide their goal of using it to replace the Western fianncial system. As the chief sharia advisor to HSBC wrote, in a 2002 book: "For a non-Muslim state to have more pomp and glory than a Muslim state itself is an obstacle, therefore to shatter this grandeur is among the greater objectives of jihad." Western governments, financial institutions, and publics have yet to understand what is going on.