> unsolved double spending problem and provide true, distributed, open-to-all decision making

This seems to be the fundamental piece of Bitcoin dogma that still gives a modicum of hope to Blockchain enthusiasts. Let me try to get the record straight:

Firstly, “Bitcoin” is not tied to any blockchain by the laws of physics. Some people call the BTC blockchain “Bitcoin”, some people call the BCH blockchain “Bitcoin”, and some people call the sum of both UTXO sets “Bitcoin”. Some even call the set of all forks that originate from Satoshi’s genesis block “Bitcoin”. To wit, there is no set-in-stone definition of which blockchain is “Bitcoin” in the event of a fork. Some think it’s “most POW”, others say that’s not true because users can change the POW algo to escape from centralized miner takeover. The latter camp will argue that the fork that the economic majority call “Bitcoin” is Bitcoin. Some will say Bitcoin must use SHA256, others will disagree. Some say that the 21M supply cap is a defining characteristic of Bitcoin, others will say that if the majority of the network wants to change it to 22M, then that’s the new Bitcoin. So I think it’s clear at this point that Bitcoin is not tied to any one blockchain and is actually determined by social consensus.

Here’s a thought exercise: Say exactly half of the investors think a hard fork should be done to make Bitcoin fungible and anonymous (like Monero), but the other half disagrees. If such a fork happens, there is a social struggle to establish consensus on which fork is “Bitcoin”. It is impossible to accurately measure which side is “winning”. Maybe you can do Twitter polls to ask people which blockchain they think is Bitcoin, but we all know that such surveys can be trivially manipulated. So there is no robust way to mathematically determine which blockchain is Bitcoin. You may believe “BTC-Fungible” is Bitcoin but you have to understand that someone else, or the majority of the market even, may disagree with you and believe that “BTC-Non-Fungible” is Bitcoin.

A historical example: In 2013, due to a bug, there were 2 Bitcoin blockchains: the v0.8 blockchain and the v0.7 blockchain. For the time during which the 24 forked blocks were being mined in parallel, which blockchain was Bitcoin? The most reasonable answer is “both” but admittedly it’s not clear. Others would say it was v0.8 because it had more hash rate? But then Bitcoin just rolled back after 24 blocks mined? That doesn’t sound very immutable...

Anyway, this is where double-spending comes in. When the fork was happening, double spends could be done easily without having to be or work with a miner. Just send the merchant Bitcoin on the v0.8 fork. Luke DashJr could have easily done this since he’s the one that called for that chain to be dropped. Then, when the social consensus resolves on v0.7 being Bitcoin, it’s too late (24 blocks): the merchant already accepted your v0.8 tokens and you’re free to spend them again somewhere else on the v0.7 chain.

In conclusion, proof-of-work consensus does not rule Bitcoin, social consensus does. Double-spends are easy to understand when you talk about Bitcoin as being a God-given or set-in-stone ruleset. However, the rules of Bitcoin are in constant flux, determined by the market. This makes double-spends a social problem, not one resolved by code.