However, given the way that Bitcoin works, I really wonder if governments do want to shut it down. This may be controversial but it seems with the blockchains the psuedo anonymity of bit coin that the transaction history (if its used primarily for crime) is creating something of a map of nodes as to who the 'big' guys are and who the 'little' guys are. This isn't an 'id' based strategy more along the lines of 'where has this bitcoin been' and then tracing all of them to see how they flow. If all you do is download transaction blocks once a day and note which coins have transacted, then compare that with the coins you find in the wallet of the guy you just arrested, it might leak more data than you would hope. Pure speculation though, based on how current law enforcement identifies criminals by watching bank balances change.
[1] They had great properties, you could take them into any casino and get their face value in dollars.