This is one of those questions where a rebuttal and an explanation would be extremely long, and would also have to work against your biases/beliefs. I hope someone more eloquent than me comes along.

In short it's a complicated matter, with tough constraints.

For one, yes banks do concentrate wealth a lot more than Facebook and google. HFT/prop desks/Cdo desks and the firms PE and IB arms are extremely well paid. They concentrate wealth very effectively.

They are doing something wrong, and from the emails which have come out its clear that the extent of it is literally unbelievable. As in the wrongdoing is so obvious, that people can't believe it's happening and move on.

I cant offer you too many links, because I don't keep a list of all the evidence the banks churn out, but the recent libor trader emails are a great start. You can follow that up by reading about the magnetar trade, or abacus - where Goldman Sachs sold their customers a CDO all the while shorting it because they knew it sucked. Edit: After that the emails where they forged ownership documents of mortgages would be illuminating.

The mechanisms are failing us, and the financial industry is extremely good at dancing on the edge of the words, but completely outside of the spirit of regulation.

Further regulation has been reduced, most notably glass steagal in 1999. We are actually seeing the crisis because of a proliferation of financial institutions and instruments caused directly by deregulation. Which is exactly what you are asking for. (edit: this also brings us to the edge of what we can discuss in general terms - you could mean deregulating so that we get a 100 bank of America's)

At the same time the regulators have been understaffed and weakened, so malicious actions are easier to get away with.

On top of all this, there is a chasm of understanding between a lay person and the rituals of wall street.

It was news to me that if the sec says its going to take a bank to court, it means the banks usually will settle.

The sec has few resources, so they choose cases where they know they can make an impact and not waste effort/respirces. when they do tell someone they are in their cross hairs, it's enough for people to realize "ok, we better dial it down". If they say they will take you to court, it translates as "the sec knows they have evidence against you, likely sufficient to get a judgement"

To this most banks immediately plea bargain so that they pay a fine, take measures to correct it, and importantly - don't have to publicly admit to wrongdoing.

Banks work very hard to make sure they don't have to say they broke the law.

Only Goldman recently was arrogant enough to fight the sec and they lost. It was one of th largest fines in the sec's history, and yet it was a drop in the ocean for GS.

This matters because wall street is treated and reported in the main stream press using normal language. The reality of what's going on if translated better is hair raising.

As people are commenting "anyone with a Bloomberg terminal in 2006, knew that libor was being manipulated"

Edit: honestly once you talk to a few traders or just keep up to date with finance news it starts becoming revolting. Many things are open secrets but are artfully reasoned away each day.

Also, banks is a huge term for what they do.