Authorities always want to strangle that which they cannot control.
But the Bitcoin train has left the station, and it cant be stopped. They could shut down Gox, BTC-e, XYZ exchange whatever, new ones will pop up like its a game of wack a mole:
http://en.wikipedia.org/wiki/Whac-A-MoleFurthermore, you will ALWAYS be able to buy Bitcoins locally from the people who mine them:
https://localbitcoins.com/They cannot stop the BTC transactions themselves from being conducted. They can disrupt Bitcoin and try to slow its growth down, but it cannot be stopped, period.