The fundamental purpose of Wall St.is to provide credit to the manufacturers of goods and providers of services of the real economy. This is actually pretty mundane business. Mainly underwriting stock sales, and bond issuance for real companies. Oh, and creating the money supply, by fractional reserve lending, we can't forget that ;-)
But Wall St isn't satisfied with providing a service that is needed by our economy. No they have to create other gimmicks to fatten their wallets. First they take the occasional merger or acquisition and change that into 'me too' waves of one or the other. Then, they create venues for speculation. Then they create new kinds of securities called derivatives, and they get into businesses where they have no business being like mortgages and insurance. Finally, they leverage all of this with their ability to create money out of nothing enabled by their friends at the Fed and Treasury. Of course, all of this slight-of-hand has to come to an end.
So, when it does, Wall St. makes sure that they are protected. They threaten to hold the economy hostage unless the government hands over what they want. ie. these are the Financial Terrorists. The government readily complies as not wanting to upset their friends and future employers. Besides, the US has lots of hard working people who the government can tap for decades to pay of this bill.
And so it goes. The Biggest Shakedown in World History!