If governments succeed to ban the use of Bitcoin within their realms, as I'm sure that some will, so what? Has the illegality of contraband actually stopped it's trade in meatspace? By what method would the government actually be able to stop Bitcoin's trade in netspace?
It is true there would be a huge problem with enforceability. But if Bitcoin is relegated to only the black market online - you can use it but don't let anyone find out - that would hamstring it. Bitcoin would never reach its full potential. I for one think it would be delightful to be able to pay for goods on Amazon or even the local grocer in Bitcoin.
And there would be a whole economy for micro transactions, impossible with conventional payment processing systems. Perhaps if it grows large enough there will be money for pro-Bitcoin lobbying.
Failing that we should all be donating a lot more to EFF.