> Git would still be decentralised if it used SQL. SQL would be a language that the git clients would communicate in - git's model would still hold. What makes git decentralised is you copy the entire codebase and then git doesn't treat the original as any more valid than your copy.

You're totally right. We're sort of mixing abstraction layers, here, of course you can implement Git on top of SQL and even SQL on top of Git! (since sql is just a query language + ACID constraints). But I suppose I was more responding to the spirit of the grandparent's statement, which was the traditional usage style of SQL. But you are absolutely correct.

> There are some interesting applications of blockchain in the examples you mention, but they are very case specific. For example, there would be resistance to creating a financial asset where trades can't be rolled back, for example (from governments and probably a number of traders).

Yes, that is certainly a possibility. However, if I were designing a financial system from scratch, I think i'd probably build in irreversibility at the protocol layer, and then allow institutions to sit on top of that protocol that implement reversible trades by delaying or abstracting settlement on that protocol. I.e. the current crypto model, where 99% of trading happens on exchanges, not on the blockchain. But, when you really do want an irreversible transaction, you bail out to the blockchain and you do it there. I think that is the most sensible model to build a modern, global financial system on.

> Legal firms might _like_ being able to destroy documents without leaving a permanent record. With source code we generally have highly trusted groups who are ideal central authorities (eg, I'm only going to get my kernel sources from kernel.org).

We do have highly trusted groups who are good central authorities, much of the time. But IMO that is something we've developed out of necessity. It's an artifact of our technical inability to collaborate with trust in the absence of intermediaries. What I think is so exciting about blockchains are their ability to alleviate that trust requirement in certain circumstances.

For instance, right now, financial institutions basically are in the business of trust. They do some other stuff too, but their course business is balancing risk and being trustworthy by having scale. JP Morgan isn't going to steal the money in your checking account, because if they steal your $10,000, they put their multi-billion dollar business at risk. So you can trust them not to steal your bank account balance.

But what systemic effect does that have? I would argue it has a centralizing effect, not just of trust, but of economics and innovation. If you have $10,000 to put in a savings account, you're not going to entrust it to a bank that only has $20,000 of deposits. Because they have a decent incentive to run away with it! This means that these sorts of institutions have very powerful incentives to grow ever larger, and be extremely risk averse. That is, they are incentivized not to innovate, because innovation is risky, and risk is trust-destructive.

Blockchains represent an opportunity to break these sorts of anti-competitive thickets, that rely on this intangible trust-asset to keep out competitors, in very much the same way that the internet helped say, blogs, compete with newspapers, by democratizing distribution. The internet democratized distribution, blockchains democratize trust.