The world gets uncomfortable when dominating amounts of creation and flow are controlled by the same person or company.The notion of separating securitization from market making is intriguing from a regulatory standpoint...
Thus, Amazon can dominate the selling of books but it will be bad if they take over publishing, as rumor has it they would like to do. Similarly, Hollywood shouldn't control the TV channels, to take a very outdated example. And securitization and market making should be done by different companies too.
There is perhaps a sort of anti-Heisenberg principal (anti because it has an upper bound rather than lower bound on the right hand side) that says that if the product of creation and flow controlled by one entity (person or company) gets too large, it becomes dangerous from the point of view of both that one entity and from the point of view of the entities it serves:
[Principal] [Agency] < h
[Creation] [Distribution] < h
where h is a constant, say (30%)^2 that shouldn't be exceeded. You can have a lot of one and a little of the other, or vice versa, but not a lion's share of both.
Lessons of the Fall, Emanuel Derman's Blog on Wilmott.