> if mutability and trusted third party oversight is actually usually a necessary and desired fraud prevention feature in a payments system, there's probably not huge demand to replicate all that using blockchains whose most-touted virtue is immutability and trustlessness
This is exactly right. Once you empower trusted intermediaries to police and reverse transactions, you lose cryptocurrency's primary raison d'être.
I buy a shirt online using cryptocurrency. The merchant teams up with an intermediary to ship it to me.
I buy a shirt online. I team up with an intermediary to verify that the merchant ships the product as promised in exchange for a small fee.
I buy an electric skateboard online. I view reviews written by intermediaries about their experiences and watch some videos those intermediaries have posted of them riding the boards over various terrain.
I make a transaction where I am asked to commit money upfront without receipt of any goods. I use an intermediary (escrow service) to hold the funds in a specifically sanctioned way, to avoid the risk that my counter-party is dishonest.
None of these things are replaced by the core mechanisms of a cryptocurrency. Cryptocurrencies just make some kinds of trust more efficient to establish, but it still must be established and in most cases cryptocurrencies don't offer mechanisms for it. Ethereum does, but in a way that necessitates trusting the behavior of smart contracts, so it's a building block for efficiency and scale, but not a replacement to the core human institutions that involve intermediaries.
None of those are intermediaries that police and reverse transactions. Even escrow services do not offer the same protection as credit card chargebacks, which go out to 90 days or longer. Once you implement that type of intermediary, the primary raison d'être of cryptocurrency -- decentralization and immutability -- goes out the window.
I take note that you have reduced the claimed value of cryptocurrency from decentralization and immutability to mere "efficient trust establishment". However you are still making a totally unsupported claim that it is more efficient that existing methods (e.g. getting a credit card or payment processor). Considering the enormous energy cost of mining you will need to offer some support for that. Otherwise it's just frothy hype.
This is exactly right. Once you empower trusted intermediaries to police and reverse transactions, you lose cryptocurrency's primary raison d'être.