Yes, I imagine that would be counted as stealing, if it wasn't intended.

However, if the bank had spent large amounts of time absolutely promising irreversible transactions, and publicly opened itself to attackers, then - no, that's just an intended operation of the system.

This is akin to going to an ATM and finding a bug that lets you withdraw money out using the information from a receipt that someone threw out in the trash bin. It is definitely illegal.

If you find a way to get the ATM to spit out $100K to you by mistake, legally you have to pay it back. Same if it’s the bank’s error.

Sure, but banks and ATMs have never declared that code is law

Has Nomad ever said "code is law"? I really doubt they did.

I'm not sure if it's theft but they most certainly have to give the money back. It's just an honest mistake, an equivalent to accidentally dropping a wallet full of cash on the street.

But that wallet has a signed, notarized affidavit that says "finders keepers".

But there’s a fair chance that the courts will eventually declare this style of affidavit invalid, being trumped by some law or other.

But if you allow the courts to dictate which crypto transactions are legal/illegal and to undo illegal ones, what's the point of all the decentralisation? You can just use the existing systems.

Which country's laws apply? What if one country considers the Ethereum contract binding, but the other doesn't?

It feels like having your cake and eating it too. I met lots of crypto bros, they all talk about how they use it so they can be immune to government censorship/intervention etc. They gloat about using crypto to avoid taxes and laws.

Relying on the same institutions that you are trying to get away from to overcome flaws in your framework seems entirely hypocritical to me.

And therein do you see the almost inevitable doom of the dream of decentralised cryptocurrency, because it’s never going to be able to stand up against the power of governments once they decide they don’t like it and have no vested interest in it surviving. All of this stuff, even up to Bitcoin, is only still around at the sufferance of governments that have not yet decided to clearly make it illegal. Most are currently preferring to regulate it (which does tend to undermine the principles of full decentralisation, as you rightly observe), but a few decide to cut it out like a gangrenous parasite that’s enjoying mixing metaphors too much, and others may at almost any time. Already cryptocurrencies flout things like copyright and privacy law, for they have made it fundamentally impossible to comply with various plausible court orders. And “we have designed it so that it is not possible for us to comply” does not impress courts.

And in your musings about which countries’ laws—therein also do you see the perennial mutterings of discontent at international policy, and globalisation shambling towards collapse. It may be averted. It may not.

Unfortunately they won't be able to do much about it, besides jail someone (who may in fact be unable to make the victims whole).

When the executives of cryptocurrency firms start getting jailed for contempt of court (when they fail to comply with a legitimate court order), the industry will collapse, which will take the value of cryptocurrency with it, which will return cryptocurrency to niche status, even if the governments in question don’t just decide to make it illegal.

This may not be the way things unfold, but it’s legally completely plausible.