> What do you propose other than a block chain for the public ledger?

A csv file, SQLite file, mysql database dump, ... The blockchain is a distributed, trustless ledger, which is not necessary for most applications.

If I may paint a picture of why this matters with an example from the gaming industry - simply because I'm familiar with it: There are projects being made where the inventory/achievement/whatever system lives on a public blockchain, so that you may use/display it in another game, website, whatever.

But this already exists without blockchain! If you play Spiral Knights or Half Life on Steam, you get a hat in Team Fortress 2. There are various third-party websites where you can display your Steam/Team Fortress/Dota/LoL achievements, inventories, ... because those 'ledgers' are public already. You can trade Steam items on third-party websites (which interfaces with steam underneath) that dodge Steam's 30% store tax and will actually pay money out unlike Steam.

The above applications only require public (or even just shared) ledgers. Distributed and trustless is not a requirement for these use cases.

> And if your system uses cryptography for the transaction security and has a public ledger, why would you not call it a cryptocurrency?

You could just as easily transfer USD, GBP or EUR using such a system. The currency itself need not be 'crypto' for the system itself to use cryptography for transactions. You wouldn't publish such a ledger for obvious reasons, but technically you can.

> If you play Spiral Knights or Half Life on Steam, you get a hat in Team Fortress 2

A centralized MySQL database is not a "public ledger" in the same way that a decentralized blockchain is considered a "public ledger."

In the former, the database can be removed or censored easily by the central entity controlling it. This includes issuing API keys: the central controller decides who has permission to access, use, modify, and even retrieve the data.

In the case of a "decentralized, permissionless, public ledger" blockchain, no single entity controls the data structure.

> A centralized MySQL database is not a "public ledger" in the same way that a decentralized blockchain is considered a "public ledger."

A public ledger is just that, a public ledger. It need not be distributed nor trustless to be public. The novelty of blockchain is the distributed and trustless, but most applications (as I outlined in the example above) only need to be public.

Trust me, I understand that a database dump is very different from a blockchain ala bitcoin, in exactly the ways you described, but that doesn't mean we need to shove blockchain everywhere.

I concede with this and your earlier point, you don't need a blockchain to build a new banking system. The current banking system is evidence of that: there is no blockchain needed when you ask your bank sends your funds to another bank.

But if you want to build a system that is not wholly dependent on "banks" and centralized actors securing consensus of financial transactions - which is effectively Proof of Authority - you end up having to look at alternative consensus mechanisms like Proof of Work or Proof of Stake.

The same logic applies to something like game assets. People buy and sell game assets already without a blockchain, but they do so only through centralized custodians and intermediaries.

>But this already exists without blockchain! If you play Spiral Knights or Half Life on Steam, you get a hat in Team Fortress 2. There are various third-party websites where you can display your Steam/Team Fortress/Dota/LoL achievements, inventories, ... because those 'ledgers' are public already. You can trade Steam items on third-party websites (which interfaces with steam underneath) that dodge Steam's 30% store tax and will actually pay money out unlike Steam.

That ledger is controlled/can be edited/changed by Vavle. Valve can delete your inventory and there is nothing you can do. Wouldn't that defeat the purpose of having a public ledger that no one can modify on a whim?