On what legal grounds?
Maybe in a totalitarian communist regime bitcoin can be made illegal, but in the free world a legal case would need to be made. I have never heard one, have you?
You don't need to live in a totalitarian and communist regime to experience banning of something. In EU for example, laws have been voted to ban glyphosate (Monsanto Roundup) use for example. In some countries of the free world some gov's plan to make the use of a bicycle with helmet illegal so why not BTC ? If a government judges it as a tool for money laundering they can decide to vote a law to make its use illegal.
Your examples all have sound reasoning and legal justification. Round-up should be banned. It is unproven technology that could have devastating effects on the future of all plants.
A bicycle helmet is required to ride the bike paths and roads where I live. Why? Because the government owns the roads and as such they can make rules to keep the roads safe.
As for money laundering, that is already against the law and the gov can do whatever it needs to to stop money laundering, but not just ban bitcoin because it COULD be used that way. Just as the gov can't ban baseball bats because they could be used to beat children.
Maybe not all of them, but legitimate governments need a reason to ban something.
If people are using it for unfair it is not the fault of bitcoin it totally depends on the user and governments can make checks on the transaction and investments rather than to ban such a profitable business and ban is not the solution to the problem the true investor will suffer this decision and bitcoin never wants to let down its investors.