when participants don’t trust each other, they delegate to a third party they both trust: a bank, a notary, an external accountant, etc.

Blockchain provides nothing, and people end up building replicas if real-world trust systems around it (even silk road had a reputation system not built on blockchains)

None of that has to do with blockchain. You as a human have the same trust in something.

In this case, instead of a verified, regulated, audited central bank, you've decided to instead trust anonymous, unaudited, unregulated actors who vote in majority.

There's a difference between trusting a human with your money, and trusting that you correctly understand an open system which fully incentivizes everyone to operate predictably.

It's the difference between trusting Facebook to keep your messages private and trusting PGP to keep your messages private.

Yea, that difference isn't relevant here, and your second sentence is not an example of the first. We know the encryption works but nothing about blockchain/bitcoin incentivizes anyone to operate predictably.

Humans are soft, irrational and messy in interactions. This isn't compatible with the perfectly technical math-based operations of bitcoin as a currency, and that's after they choose to trust it in the first place.

I mean sure, there's always the always the possibility that a majority of miners ally together, forfeit millions of dollars of mining rewards, and likely cause all of their cryptocurrency holdings to plummet in value, all in order to double-spend a few of their own transactions. But if we're going to worry about the possibility of everyone involved becoming irrational, then I'm going to worry about the more realistic scenario of my bank doing something surprising with my money and causing me to go through legal hell, especially if my lawyer and the judge decide to be irrational too since we're comparing against a case of whole groups of people acting irrationally.

It's also worth mentioning that Bitcoin and Ethereum have never had a 51% double-spend attack. People do occasionally go through legal hell related to their bank/paypal/whatever accounts, or have problems sending money through their bank to who they want to send it to.

It's not about all people being irrational, it's about humans having negotiations and softly defined deals when it comes to money. Bitcoin doesn't fit this scenario like human-powered trusted authorities do.

There's a reason why the legal system exists to offer you the case-by-case evaluation when needed. Many people have lost money through bitcoin, through hacks or poorly coded contracts, or to scams, or directly funded criminals and terrorists. Those people would have much preferred a little "legal hell" as you call it rather than no recourse at all.