The main problem, IMHO, is that the banks have grown so large that it
matters to us how they operate their business.
Taking nickbat's shopkeeper analogy, if a shopkeeper decides to operate his business in a risky manner, he'll either get rich or go out of business. We wouldn't care either way because there are plenty of other shops. Some might see the Bentley parked outside and shop elsewhere. Another shopkeeper will be more prudent and make a modest living, but survive in business through thick and thin. Either way, diversity means there'll probably be a shop when I need one.
We all (personally, and as a state) have so much at stake with huge banks that they can't be allowed to suffer the consequences of their actions - so, you can't be allowed to go out of business. What do you go for? modest or rich?
There is, of course, another issue that we have surrounded ourselves with politicians who are only interested in lining their own pockets. We can only hope that they haven't got such a foothold yet that they can be removed by non-violent means. Doing so would require the general populus to wake up and smell the coffee, though.