Obama's prohibition against prop trading...

...will never work.

This being the U.S.A., it cannot happen.

One disadvantage of being a "nation of laws" is that fallible humans write the laws, which are "influenced" to a large degree by those who have access to the writers (draw your own conclusions regarding this fact).

So this country is somewhat unique in enforcing laws as opposed to enforcing more "social" relationships (such as class, nobility, etc.) The "spirit" of the laws are not enforced, and in fact to do so would invite disaster. Thus, we have monstrosities like the Tax Code, the breadth of securities and banking regulations, and many other examples of massive rule books which attempt to detail what you cannot do (as opposed to what you "should" do under a more pliant standard of enforcement)

So the rules (e.g.: the law) is written with loopholes via either unintended consequences or explicitly included by way of "influence".

Obama can wax on populistically and cite some standard of "fairness" (which apparently only he understands in total), but the rules will be bent and broken. They always are.