The govt. would not ban bitcoin commerce without a very good pretext in place first. Govt.s acting arbitrarily against seemingly peaceful activities can get voted out in an awful hurry ... they need a good reason to ban it or else they just look like petty tyrants ... perception is everything.
Unless all governments ban/regulate bitcoin, it will be seen as a success in the nations where it is allowed and it's value will be backed by their economies. Also, such nations will thrive on a sound money standard.
The rest of the world will see this and soon governments will be force to come inline and legitimize bitcoin.
why would they need to ban it if every country in the world has already given its central bank the monopoly on issuing currency and made all other currencies illegal? in the "spirit of the law" bitcoin is already illegal everywhere. some of the laws might technically not include digital-/crypto-currencies but they will likely change that swiftly once they wake up.
It's just ridiculous to think of the big brave govt. thugs showing up with the machinery of the state, paid for by the tax-payers, raiding the homes of gamers living in their mom's basement, to cart away their "illegal video game rigs". Who would even think to ask such a question, govt. paid foil, statist troll, failed bankster .... I wonder?
they wouldn't (need to) do that, or only in some extreme cases. if bitcoin grows over critical mass to wake them up they will make exchanges between bitcoin and fiat currencies illegal, they'll threaten any financial institution that engages in such exchanges, and they will generally make all bitcoin transactions illegal. they might go after the users or they might not. the exchanges are the critical point (at least until all fiat currencies disappear) - that's why i believe bitcoin needs a working underground peer-to-peer exchange system asap to survive in the long run (was proposed in another thread somewhere). they wouldn't be able to control that or enforce their laws once that exists. but reaching mainstream adoption will be very difficult this way, eg the majority of online poker players wouldn't wanna go through these hoops.
not trying to burst your bubble but to inject some realism! bitcoin has the power to severely disrupt the core of the current capitalist empire. you might be too naive if you think the empire will not strike back. it will with full force, better to be prepared for it and find solutions to overcome it than to keep dreaming imho