Actually Delta1 desks earn because they have low cost of capital, huge balance sheets, and can avoid the "toll booths" to the markets that their customers can't. At the end of the day, their customers lean on the Delta1 desks balance sheet and then the delta1 desk can hedge the risk out cheaply in the market. It's not about manipulation scandals, though some of that happens (front running and not passing best execution); its about scale.