If you are going to draw attention to your identity and credentials, and also ask the other party to engage more kindly, maybe you shouldn't categorically call

If you are going to draw attention to your identity and credentials, and also ask the other party to engage more kindly, maybe you shouldn't categorically call the people you are engaging with "idiots" on other platforms, especially given your profession is education. Credentials also are not a proof of understanding something. Your analysis of git makes complete sense to me. I understand how git uses hashes and merkle trees to prevent tampering of data. It is also a good analogy in that bitcoin uses similar properties. I am furthermore perfectly happy to trust a single authoritative source (or trusted peer) when initializing a git repo, it works better that way. But git is not solving the same problem as bitcoin. You concede that PoW is a solution to this problem, but that it is "unnecessarily costly". But you haven't given a solution to the problem that costs less, only argued that in practice the problem has assumptions that are in practice not necessary. You seem to believe that bitcoin without PoW could still in practice arrive at a consensus through either being able to check that a last block hash is the same as the "real hash", or that you would be able to compare your value to multiple sources. These ideas both rely on another consensus system outside of what is promised by bitcoin itself-- either a trusted third party to enshrine what hash is "real", or being able to rely on a consensus merely based on some number of network peers. Number of peers will not work by itself, because there is almost no cost for an attacker to create many dishonest peers. Note that the purpose of an attack of this kind is not merely to defraud users of bitcoin, but could also be a denial of service attack. Seeing peers with different blockchain history would make the network unusable. I also don't understand the hangup over PoW and immutability. Immutability is the concept of data that is not changed. If you have a more precise definition, please give it. This could be split into the idea of a design principle, versus the idea of enforcement of immutability. E.g. using an immutable data structure in a trusted programming environment does not need enforcement. We are only talking about the enforcement aspect. A hash digest is a really strong, almost perfect enforcement-- finding a collision is in practice impossible. A digest hash only guarantees that "if trust the hash, I should trust data that matches the hash also". On the otherhand, PoW does act as a soft form of immutability, using economic barriers rather than cryptographic guarantees. PoW guarantees that "this data could not have been produced, and could not be further changed without expending some amount of physical power, and therefore there are unlikely to be variations of this". This effect is orthogonal to the internal immutability provided by hash digest / merkle trees.