But most of the bans are not retrospective. If government bans bitcoin today, it doesn't mean I will be prosecuted because government can track the trade I made yesterday. So unlike gold, I have a clear working plan if bitcoin gets banned. I can immediately send all my bitcoins into hiding using mixers. I can even sell them in disguise. All these features weren't present in case of gold so government could easily locate the person if he tried to sell gold in market. With bitcoins there isn't such problem.
I don't think it won't be that easy for someone who doesn't take his/her privacy seriously, but it completely depends on how far the government would like to track your funds. For instance, if you bought bitcoin and sent it to a mixing/coinjoin service, they
might prosecute you for that. Yea sure you could tell the authorities that you already don't have access to the funds, but you get what I mean. It's definitely doable, but can be difficult for some.