What is a currency? A currency is a unit of measure, which is used to facilitate exchange. Does it matter who issues the currency or where it comes from? It does not as long as the parties doing the exchange agree on the terms. Bitcoin is an example of a currency. There are infinitely many currencies that have existed in the past and more will exist In the future.
Does the fact that some governments ban the use of Bitcoin, others allow it and others want to regulate it seem inconsistent? This demonstrates that the fate of a currency will depend on what the consensus agrees to. That consensus is generally the users of the currency.
Why did Bitcoin get as large as it did in the first place? Currencies are based on exchange - but the widespread use of a currency is based on trust and faith in the issuer of the currency. The trust is that the value of a currency is represented by actual resources that can be accounted for and used as collateral in an exchange should that become necessary.
As an example, I agree to buy apples from someone and they give me a memo stating that they will pay me in oranges. These oranges are represented by 10 units of the U.S. dollar. I am banking on the fact that those 10 units of the U.S. dollar are backed by some entity that is accountable, and I can exchange those units for the oranges that I originally wanted to buy, in the case the U.S. Federal Reserve who is acting on behalf of the U.S. government. Ten units of a currency are useless unless they can be translated into something I want to have. This is true for every currency because the currency acts as a measuring stick, a translator and a unit of account for the resources and goods that seek to be traded. If you measure something in inches or centimetres, the thing being measure is still the same size.
How is this related to Bitcoin? It shows that currencies like this can spring up anywhere and anytime as long as they adhere to the rules above. More currencies like Bitcoin have been used in the past and will be used in the future.
Disclosure: I have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.