They don't need to ban it directly to outlaw it. What if fiat money made off of selling cryptocurrencies were declared illegal? Even if you had billions of bitcoins, they would be worthless because you wouldn't be able to cash out legally.
But that is what people are failing to understand I feel like. You don't need to cash out once you have all the Bitcoin because you can spend that as currency. Everyday it becomes more spendable yet you want to cash out to the ever weakening purchasing power fiat currency? Yeah right, I will stick with my Bitcoins for the rest of my life, you can do whatever you like
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