EDIT: thx to everybody who replied! That being said, I would have really liked to discuss the actual technicality of blocking a cryptocurrency :-) E.g. what technical measures could a hostile government take against bitcoin and how would any circumvention techniques, if they exist, impact scalability and usage of bitcoin. A lot of answers here just give reasons why a govt would never do something like this; or that there are other ways of discouraging bitcoin users; or that it wouldn't affect users outside of that country (wouldn't it though?). I think the dependence of cryptocurrencies on IT infrastructure is an important issue, as it puts boundaries on the extent to which a cryptocurrency's can truly be considered decentralized. I think we should assume that, given enough time, any cryptocurrency that makes it to the big leagues of being used as transaction money will be put to this test. And if it fails this test, its use cases will be more limited than what some currently think.