But if you look at other cryptocurrencies like Etherium for example, you'll see an interesting differentiation. Not all cryptocurrency values are tied to Bitcoin. Etherium, at the time that I write this, is up 2.4% over a month ago while Bitcoin is down 37% over the same period.
So, while I do think Bitcoin especially is pretty much definitionally a bubble, crashes and volatility are the nature of the game right now. We should be careful to lump digital currency as a whole into the the same category as Bitcoin. Bitcoin was the first, but probably wont be the last and certainly isn't the best.
I think there is value in cryptocurrency that is difficult to see for many people past the black market stuff and the gambling aspect people put to it. If you've ever transferred Etherium to a friend to pay them back for the pizza they bought you, you'll feel that value in a small way.
I'm certain there is a reason these currencies exist beyond the sketchy reasons and I'm quite sure they are here to stay, bubble or not. There was a massive housing bubble, but we still have houses and they are, mostly, recovered above the peak of that bubble ten years later.
It's not hard to imagine a (near) future where cryptocurrencies are a primary means of monetary transactions.