from the main wiki page, 3ed point under the title "why?":
Quote
Be safe from instability caused by fractional reserve banking and central banks. The limited inflation of the Bitcoin system's money supply is distributed evenly (by CPU power) throughout the network, not monopolized by banks.
As many of us know, the above mentioned fractional reserve banking, central banks, inflation and banks monopolies are political instruments serving the interests of powerful entities. Never in the past have those powers hesitated to protect and secure those interests using all means (financial, PR(opaganda), legislation and even wars). While I'm reading all kinds of analysis on the technical ability to shut down the network, with terminology taken from the file-sharing-war (port blocking and deep packet analysis of ISPs, analysis of the public blocks data to identify wallets and IPs and so on), it seems to me that the real threat to Bitcoin and the easiest way to kill it is to target the exchanges. We've seen how easy it was for paypal to cancel (and even confiscate the funds of) paypal-to-bitcoins exchanges. They didn't even need the help of senator friends or the terror \ drugs \ laundering excuses. What if banks will do the same? Clearly they'll have the motive and means. Can Bitcoin survive a simple ban on exchange? Do you find such scenario probable? Do you foresee others?