That number sounds trivial for even a very wealthy private individual to get them each in a vulnerable position.
For example, how many are in China or the U.S.’s reach? Because that means literally two people, Xi and POTUS, could round them up and effect a change. (Not saying they would. But a damning vulnerability for a libertarian ideal.)
Incentives are actually an important part of the equation. Why would a wealthy individual or government spend billions of dollars to do a 51% attack? There's basically no incentive to do so. The best they could achieve is to censor transactions for a while until the Bitcoin community decides to fork to a slightly different PoW algorithm.
China has banned cryptocurrencies [1]. So there is precedent. (Until recently, I believed nobody had an incentive to mess with cryptocurrencies. They're too niche and too attractive as a revenue source.)
> best they could achieve is to censor transactions for a while until the Bitcoin community decides to fork to a slightly different PoW algorithm
In the scenario that close to 50% of Bitcoin miners and a similar fraction of Bitcoins become possibly (though not irrefutably) state controlled, you're claiming it would be trivial to just fork them away? Who makes that decision? If those people can just uncoin wallets of their choosing, why bother with a cryptocurrency in the first place?
[1] https://www.nytimes.com/2021/09/24/business/china-cryptocurr...
China's ban on crypto had very little effect on Bitcoin although a large share of the Bitcoin mining used to be located in China.
> In the scenario that close to 50% of Bitcoin miners and a similar fraction of Bitcoins become possibly (though not irrefutably) state controlled, you're claiming it would be trivial to just fork them away? Who makes that decision? If those people can just uncoin wallets of their choosing, why bother with a cryptocurrency in the first place?
First, let me preface by saying that I find this scenario very unlikely. China might have had the ability to do it at some point but no longer now that all the miners have left. USA now has the largest share of the mining power but it can't just suddenly seize all miners to perform a 51% attack due to the way government works. At minimum, a law would have to be passed and the miners would have already left the country by the time it did. Finally, the US does not even have 51% of the hash rate (about 35% currently).
But let's say it does happen. The vast majority of the community (exchanges, merchants, users, etc.) would likely move to a hard fork with a slightly changed PoW algorithm that would render all those seized miners obsolete. Governments and wealthy individuals know about this possibility which gives them even less of an incentive to pursue a costly 51% attack.
We still don't live in a dictatorship, the President alone can't do this.
One can imagine scenarios where the President would have the power, motivation and even duty to do this, e.g. in times of war or other exigent circumstances. Point is, this sort of concentration opens up Bitcoin to concrete routes of attack which were previously purely hypothetical.
Actually, that's exactly what Xi (or the CCP, if you like) did[0] a month ago.
[0] https://www.reuters.com/world/china/china-central-bank-vows-...