I'm giving up. Here's why:
I was thinking a bit more about the choices of the government. My assumption:
In the best case they will allow the use of cryptocurrencies under the condition that a central bank controls their money supply.
is not very plausible.
Even if money supply could be adjusted by a central bank, it would not be attractive for any government to support a cryptocurrency with decentralized mining. Where would the benefit of such decentralization be if the formula for money supply was centralized?
They'd be better off by mining on their own, probably pegging it to fiat and distribute the cryptocoins just like they do with bills and coins. This - of course - is very far away from bitcoin protocol.
This solution would even save a hell of a lot of energy consumption by the miners that will by then have risen to globally significant levels together with market cap. (See:
Energy consumption could become an issue if bitcoin really breaks through) This consumption would be futile because it can no longer be justified by the benefits of decentralization. (And I doubt this justification anyway, because there are alternatives to proof-of-work....but that's another topic)
So I agree that bitcoin will stay bitcoin, even if it will become illegal. Even if it's value drops to zero.
Thanks for the discussion.