If a bank run can spread and ruin a nation, regardless of size, why are banks still allowed to exist?

Question

http://en.wikipedia.org/wiki/Bank_run

http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GWYE_enUS273US273&q=Too+Big+to+fail

Answer 1

They offer valuable financial services.

Answer 2

The f***y Mae, Freddie and the Indy Mac are now under federal supervision.  In the f***y Mae you may continue to bank normally however after $100,000 you will on recieve 50% back. This has me worried.

Answer 3

Banks are a very important part of the world's economy.