Bitcoin still hasn't been disproven to be a fad :)
The core idea of crypto currency (i.e. byzantine fault tolerance) is 2000 years old. The fact that this happens now already demonstrates that there never was any need for this and there won't be.
Of course there was and still is. The three main purposes as I see them are as follows:
1) International money transfer free of regulatory oversight.
2) Anonymous purchase and money laundering
3) Decentralized currency free of government manipulation - Bitcoin falls short of this.
Cryptocurrency is a great solution for all of these needs. Of course I agree that most currencies add little or no value to their core product, especially the ICO crowd.
Similarly, you can just say illegal purchases. The other things have been largely debunked. Interestingly, you didn't even mention the giant primary use case of buying illegal things.
No, “disenfranchisement”. Read the Declaration, it was about usurpations of the right of the people to govern themselves. “No...without representation” is the key part, not “taxation”.
That's been inverted for propaganda purposes by modern anti-tax activists.
But, in a any case, “slavery” would have to be the Civil War, the Texas Revolution, or—indirectly, by way of the previous item—the Mexican-American War.