Comment by notahacker

If you're purely focused on the GP's suggestion that the extra liquidity permitted by HFT might not generate enough benefits to the entities engaging in productive activity to warrant trading-specific infrastructure like dedicated fibre lines, you shouldn't even have needed to ask why he didn't consider this to be solved by a tech stack that uses the electricity consumption of a medium sized country to allow people to traded purely speculative synthetic assets :D (even a blockchain not computationally inefficient by design wouldn't stop arms races to be first in line to accept the trade, or the incentives to do so existing. At least regulators have the theoretical power to make life difficult for certain types of market participant)

The GP's wider point was the purpose of the finance industry is to facilitate real world productive activity. If the "decentralised" bit is isolated from that, you haven't got a decentralised alternative to financial markets.