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.
The premise in the first sentence above does not lead to the conclusion in the second sentence. Certainly Bitcoin adoption will be hampered in nations wherein the powers that be can threaten users with real violence for doing so, but this will do little to prevent adoption in locales where this is not so.
I am not sure what you are trying to say here. All else being equal, less hampering of Bitcoin adoption means it reaches more of its potential. Even if it can survive laws, matters would be better if there were no laws against it anywhere. Resistance, local or not, limits Bitcoin's potential.
Are you saying Bitcoin has no potential at all in countries "where the powers that be can threaten real violence"? In that case I disagree. I think Bitcoin has great potential even in e.g. the western world.