[Seam0nkey]

I actually think you give the parent argument just a tad too little credit. If crypto was useful as a currency (and, as you point out, if it is comparably as energy efficient as visa), that would be an effective refutation to the energy consumption argument; freeing up human resources to do something else would be a substantial net benefit of the system for society.

However, crypto does not behave to act effectively as a currency; it would be an awful idea to replace the global financial infrastructure with crypto thus the energy costs are here to stay.

[atleta]

Well, it's not enough to be useful. It should be better to justify the extra energy consumption. Especially given the climate change. Also, you forget that we actually don't yet know (no one has estimated, as far as I'm aware) the realistic consumption that we'd see with wide spread adoption. And without that, it's very hard to argue and say that it's worth it because of the usefulness. Because we don't know how much we're talking about.

So I think the energy argument fails on it's own. Also, it should come at least with strong supporting arguments claiming the actual benefits. But I do agree that cryptos are worse than the currencies we have and existing block chains (I'm aware of) don't make sense even as a distributed transaction tracking system for fiat currencies.