Bubbles can eventually have value, weirdly - their irrational nature can sort of act as a forcing function taking us out of a local maxima, facilitating the creation of entirely new unforeseeable and previously-impossible things that actually have value of some sort. With cryptocurrencies you could argue they facilitated (through smart contracts and then distributed exchanges) the creation of massively-multiplayer online gambling games with no barriers to entry for publication & interface with the financial system where people win through patience and steely nerve. You may think more-advanced open-source casinos are not good for society, but they certainly hold economic value.
If I wanted I could write a smart contract for a MMO gambling game like POWH3D and publish it tomorrow. That isn't a capability I used to have - quite a few hoops to jump through to get a game onto a casino floor, or start up an online gambling website.