If you want a full general theory you have to go to the behavioural psychologists/economists who are doing experiments on this and developing some ideas.
Instinctively:
Humans are, it seems, in the main, moderately good, when not asked to resist too much temptation. There are some who are psychologically tuned to breaking rules for various reasons. (Some of these, those who do so for their own gain, or for sadistic power pleasures tend to be known as psychopaths.)
As such, systems of regulation should be constructed so as to avoid putting people under too much temptation where possible (relying on the honour of the individual breaks down over time because sooner or later a bad/weaker individual gets the role.)
There also need to be mechanisms to identify "psychopaths" and limit the damage they can do.
Most of all though, what the current crisis reminds us of is that there is always a tradeoff between "perfect efficiency" and the "robustness" of a system.
The propagandists encouraged us to dismantle the supports and slack in the system, to "make it more efficient" so that more money could be extracted from it. This of course made the system more frail. It's really time we started valuing the robustness of critical[+] systems more.
[+] Critical usually means "really important to our way of life" but what the collapse of isolated parts of a byzantine financial system that doesn't appear to touch normal life reminds us is that critical also means "systems that in their failure can drag our way of life down with them."
Is it enough to explain what's happening? Does it replace the unregulated freedom explanation?
Generically, "freedom" is a good, but we're not truly so brainwashed as a populace that you could have created a political narrative for deregulation that relied on the notion that the poor bankers' constitutional right to lend money any way they wanted to were being infringed...
Rather, the basic argument for "deregulation" was that regulations were getting in the way of "financial innovation" that would make the markets "more productive" and "more efficient." And thus we'd all get richer.
I see those riches being bought at the price of increased fragility.
But if you're arguing that deregulation was the road to efficiency and therefore fragility, that is slightly different.
I think there may be both. Hyper-leverage and oblivion to risk seem to me to come more under the heading "excess" than "efficiency", unless efficiency is solely defined as capturing the most wealth fastest.
In any case, it's impossible to use absolutes like 'good' without a functional 'good for what?' sub-clause.
I think there's a useful inkling that this is primarily an ethical problem. But so far all of our ethical solutions have been cast as absolutes and generalities, with the result that in spite of a modest attempt at genuine populist democracy, we're still in the pre-enlightenment position of being ruled by highwaymen with unusually expensive tastes.
Perhaps a better approach is to ask a different question. If you assume that the goal is a set of universals, which include free high quality healthcare and education, freedom to be rewarded for genuine innovation, and freedom from highwaymen - what's the best way to get there?
I'm not using highwaymen as a metaphor. The fact that the theft is disguised as a financial industry doesn't change its basic function, which is to relieve people of their wealth and not to contribute to any notion of the common good, except when grudgingly forced to.
Getting into more detail about practical, as opposed to theoretical, human nature would need a diary to itself.
Consider doing the diary. Please. Capitalism searches out the darkest corners of human potential, and mainlines them.
Any Deductive system lies at the mercy of its axioms.
Any Inductive system returns only what is being looked at shaped by the boundaries and constraints of the tool being used.
"Universals" has some of the same problems as "Absolutes" when defining Goals. But it is possible to cast them as: We want to achieve [U {A, B, ... X, Y, Z}] to the extent and limitation of [u{a, b, c ... x, y, z}].
Giving us someway to get There.
But we need to think about it. Whether we choose to bring in the Enlightenment or not.
