The problem is that bitcoin (and similar) are so computationally intense to run, that the transaction cost is much higher than Visa's.
Furthermore, a currency needs a government (or similar kind of body) to manage its stability, by printing (and buying) money. Otherwise, we'll see wide fluctuations in value like what happens with Bitcoin.
Furthermore, a currency needs a government (or similar kind of body) to manage its stability, by printing (and buying) money. Otherwise, we'll see wide fluctuations in value like what happens with Bitcoin.