That issue comes on top, in different degrees varying from country to country. A concerted ban in, lets say, the the "western world" as in the Americas and Europe, or in Asia (China, Korea, India ect), would probably put a sudden end to the whole crypto thing.
But whats eating away the foundation of Bitcoin (and therefor all cryptos) is the trading of Bitcoin derivatives, without the need to own actual Bitcoin. So the trade volume can be indefinate, which totally disables any fair price discovery mechanism. (See gold and silver markets)
Thats the way to screw up cryptos without using nasty repressive laws.