Over the long-term (40-50 years) I would only call it a bubble in the sense that humanity's a bubble: yes, it may pop, but a bubble that lasts > a lifespan simply becomes reality. Over the short term (4-5 years), I think we're going to see some very bubblicious behavior and many people are going to lose their shirt, but that averages out.

My reasoning is this:

Fundamentally, the financial industry is about time, risk, and trust. The reason the industry exists is to shift productive capacity from individuals that are able to bear it now, to enterprises that may or may not pay off later, in a way that everybody who contributed to the success of an enterprise gets paid off later (when they need the funds) and gets to do it again. Currency is an information-carrying device that both lets you shift production from the consumer to the person best able to provide the service (medium of exchange) and records that a person provided valuable services at some point in the past so that they can claim services in the future (store of value). Stocks and bonds are both different ways of transferring money that people don't need now to people who can do useful things with it now, in a way that the investor can receive a payoff later. The banking system does the same, but with institutionalized, standardized practices. The insurance industry spreads risk from people who cannot bear it now across people who can; the futures & derivatives markets transfer that risk from firms who cannot bear it to firms who can.

When I look at the ICO boom of 2017, I saw the beginning of a functioning financial system. All the basic elements were in place - the ability to transfer value and claims of future value between participants, the ability for people with an excess of credit (assets) now to fund the development of projects that may pay off later, and the trust that if those projects were successful, they would benefit. It's all in a very rough form - the network got clogged such that it took ridiculous times for transaction confirmations, most of these projects continued to fail and end up worthless (I actually have hard data on this - roughly 90% of ICOs are either scams, failed, infeasible, or otherwise abandoned, while 10% are still going concerns 2 years later), there've been a bunch of hacks of exchanges and smart contracts, market manipulation is rampant, and cryptocurrency prices look like a roller coaster. Basically, we're making all the mistakes of 19th-century finance again: the crypto market looks a lot like the stock market did in the 1840s.

But we're doing it without needing any people involved in transactions. That's hugely powerful, in a world that software is eating. Finance is a $13T industry accounting for ~20% of world GDP and employing millions of incredibly high-paid people. In the sense of crypto being a cheap software-only competitor for extremely high-paid people, it's quite attractive.

And all of the problems that happened in 2017 are fixable. There are already lots of people working on the cryptocurrency scalability problem, between Bitcoin Lightning, Ethereum Casper, and new consensus algorithms like DPoS and SCP. People are working on the energy consumed by PoW, too - almost all new coins are proof-of-stake. Distributed exchanges like the 0x protocol remove the need to trust third-parties with your funds; you can keep them all in your own wallet. Continued bugfixes to Solidity shore up smart contract security. Stablecoins like MakerDAO and USDC remove the volatility of pricing in terms of crypto. Oracles provide a way to get more "facts" onto the blockchain so that smart contracts can rely on a disinterested third-party to make decisions on data. Each bubble distributes more crypto out of the hands of early-adopter whales (other than the Satoshi-coins, these account for less than 15% of total Bitcoin supply) and into the hands of ordinary people.

I think that governments if they acted now could shut down the fiat on-ramps to crypto, but I don't think they will. Too many people that use it for legitimate investment purposes, who will be very upset if they do. Government always tends to react a little too late to the social changes presented by new technology - we're only now seeing a backlash to the Internet, 30 years later, and at this point it's a little late to shut off the net even if certain governments are trying. Besides, if a technology makes the group of people who adopt it more efficient than the people who don't, the former will outcompete the latter. At some point, once people are directly selling goods for crypto and getting paid in it, it becomes too big to fail. I think that's a few years off (I expect crypto adoption to be slower than WWW adoption, because finance is more fundamental to society than communication is), but ultimately I think the ability to fund & partake in the benefits of new ventures without needing permission from Wall Street or Sand Hill Road will outweigh all the downsides of crypto.