Joe wins the Powerball lottery. Now he's set for life, with his 250 million dollars. Joe's contribution to society was purchasing a lottery ticket. There is a high demand for lottery tickets, so Joe believes that if it weren't for people
just like him, the lottery wouldn't exist and that demand would be unfilled, and everyone would be unhappy. Joe concludes, therefore, that he
deserves all the money he has, because after all, the system is just what people want and it has decided that he's worth 250 million dollars.
Prior to winning the lottery, Joe worked as a janitor, and provided a valuable and necessary function to society. He made $10 an hour.
Now, certainly there is some qualitative difference in the reasons society valued Joe at $10 an hour before he held the winning lottery ticket and $250 million afterward.
Certainly we can say that there exist a range of reasons that one might benefit from a system, and that "people will pay for it" can be used to justify just about anything.
And the financial industry that people are upset about is not really the banks that provide loans (although there is some blame in the instances when people loan money to others knowing they have no hope of paying the money back). The loans existed already; without the loans there's no CDO to buy and sell.
The reason the CDO's existed was that the traditional way to make a loan and get your money back over time with interest was just too damn slow, and people needed a way to pretend the risk of a group of such loans didn't really exist and that they'd make exponentially more money in perpetuity.