While I believe that there was predatory lending and greed galore in the credit-bubble that lead to the real estate bubble, blaming the derivatives and their trading goes too far.
The complication that was the CDOs and swaps, while they were understood more or less in isolation, grew into a system that became greater than the sum of its parts.
Systems have properties that are emergent, that are not intrinsically found within any of the component parts. They exist only at a higher level of description. For example, an engine isn't a feature of valves, pistons, or any set of parts in isolation, they have to be suitably inter-connected.
But it is not just the emergent properties that caused the problems. Imo the problem is that the "credit system" was not redundant enough. In the engine example, if the battery dies, you cannot start your car. There is no fail over to a good battery or some other power source.
The lessons for the future imo are:
1) Complex systems are emergent and you cannot understand them by looking at the parts.
2) You can damp problems by having redundant back up systems that failover when a part goes bad.
Number two above is attempted in our economics by having re-insurers for example. The problem is that not only are these systems complex, they have positive feedback, which means that if you are leveraging $1, the effect can be magnified 10x++.
In fact, it is amazing how well it works in all but the most extreme cases.
nitro