Your point boils down to "but it will be illegal." The point you're responding to that you missed was "it doesn't matter if it is illegal, people will do it." All of those are just examples of ways to avoid getting caught. They're not solutions to it being illegal, they're solutions to getting caught.
I think there’s a distinction between “people will do it even tho its illegal” and “illegality prevents mass adoption” - the government still achieves its goals if the only opportunities to transact with crypto are mired in legal risk.
"Mass adoption" is a buzzword that means "a lot of people use it." In it's purest form it means everyone uses it, but that's not absolutely necessary to consider it widely used.
There are plenty of things in ubiquitous use that are illegal in some places, or even most places. Alcohol is ubiquitous, guns are everywhere, gambling, cocaine and marijuana come to mind, people modify their cars beyond legality quite often. Lots of people do illegal financial activity as well, most people transact under the table when the opportunity arises. You can have a scenario where cryptocurrencies are widely used even in places that ban them but are so ubiquitous that enforcement is untenable.
