[mrb]

Why would the argument be only valid when compared to other decentralized, trustless currencies? The benefits indirectly extracted from Bitcoin mining ($1B invested in 729 companies, thousands of jobs created, etc) exist precisely because Bitcoin has advantages over other traditional payment systems.

"Does "decentralisation of currency" belong in the top 100 things to devote electricity generation to?"

I think so. If (big if) Bitcoin ever becomes so successful that 1% of the energy is spent on it, think about the massive scale of positive social and economic changes it means it will have brought: freeing people from economic censorship and persecution, reducing international payment friction hence increasing economic trade, etc.

But I think neither you nor I can envision the scale of such potential social and economic changes. It is like asking a random person from the 1890s how much do they think automobiles will change the world, and almost nobody would have predicted automobiles are a major enabler of the economic expansion of the 20th century.

Transaction speeds: zero-conf txs are at risk of a double-spend, but in practice this happens extremely rarely.