Governments could declare Bitcoin and crypto to be illegal, but that wouldn’t mean they could enforce it. That’s the case with other things, not just cryptocurrency. So, there is a distinction between declaration and enforcement. We all know that just because something is declared illegal, that doesn’t mean it can be enforced. If you really thought otherwise, you would have to think governments are all-powerful.
However, governments could certainly damage Bitcoin. By banning it, they would severely weaken Bitcoin, even though Bitcoin would still survive. They couldn’t enforce it completely, but perfection is not the relevant standard. What is relevant is whether governments could hurt Bitcoin, and the answer is obviously ‘yes’. Hence, we have another distinction: the distinction between weakening vs. total elimination.
In my opinion, the more likely scenario, however, is that governments would tax Bitcoin more. This is our final distinction: ban vs. taxation. Whether you cash out or use Coinbase, the U.S. Government will know about your crypto and they will demand their cut. They already do, so this is not science fiction. The opposite conclusion is what is not only science fiction, but it’s wishful thinking and a libertarian fantasy.