Would justification would they give to ban bitcoins in the mature and democratic countries?
Money Laundring? Well then ban banks as well because billions are laundered through them. Remember all those articles about how the biggest provider of liquidity in 2008 was the mafia?
Drugs? etc, Ban cash too then.
Moreover, if they tried baning bitcoins it would be seen as an unreasonable, even unacceptable, restriction of freedom by everyone from journalists to all sorts of think tanks and economists. Many would convincingly argue that it would hurt the economy etc.
So it is never going to happen.
If it does, then bitcoins would go underground. It would probably still be used to buy drugs but also for more seriously criminal stuff. It is after all a very fast, anonymous, safe, way to transfer wealth. So I think the price would crash as the news comes through, but then it would slowly recover as many people simply ignore the law as with copyrighted sharing, start selling it in a one to many platform rather than many to many as in exchanges. Then, as it would become harder to get because many want it, especially the black market, the price would go up and up to the point where honest people might even be willing to risk prison to have one.
And that would be the best argument in my opinion against making it illegal. First, it would hurt the economy quite badly as innovation is being stopped, thus the economy would not become more efficient. Secondly, it would take the benefits of this innovation and efficiency away from honest hard working people and drive it underground, because it certainly is not going to make it vanish.
For those reasons, I do not think the government can or will ban bitcoins or overtly interfere with its development.
I agree with every sentence except the last one. I think the best thing for governments to do would be to accept Bitcoin and even encourage its growth. But I also think governments have a track record of not making sensible decisions.