> Property rights are a social construct [...]

Right. So expecting a social informal construct to be enforced in an automated way is, to put it mildly, difficult.

> Sure, it may be difficult, in some situations, to prove ownership of the stolen cash or to recover it.

How do you exactly prove ownership of money? It seems a bit more than "difficult" to me.

> maybe this explains why many people seem to prefer electronic payments over cash

And just as many people prefer cash over electronic payments. It still doesn't mean that cash is, in any way, fatally flawed.

> It might indicate that indeed cash is perceived as being less safe.

Well... different people have different opinions and perceptions. Just because most people use electronic payments (let's assume) doesn't mean that cash is useless or fatally flawed as a medium of exchange. And just because most people use cash rather than blockchain thingies also doesn't mean that these are necessarily fatally flawed.

> Now, back to blockchains. Blockchains are very inefficient and expensive to run. This is so, because they have to do a whole lot of extra work in order to avoid relying on a central authority that ultimately has the final say on who owns what.

Sure.

> If blockchain users have to go to court to have property rights enforced,

Of course they have to go to court to see their property rights enforced. Rights/laws are always enforced by humans, not by automated systems.

> that means that the courts do have the final say on who owns what, and so the entire purpose of the blockchain, which was to avoid a central authority, is defeated.

Not really, since courts do not have global jurisdiction. If I steal your crypto-assets and we're both in the same country (and you have some proof of ownership and whatnot), then you can go to a court and get your assets back. If we're not in the same country, you probably won't be able to.

The same way that, if someone steals my money (or any other asset) and flees to another jurisdiction, I probably won't be able to do much.

If entities A and B are in the same jurisdiction, then courts can compel A to give something (that was stolen) back to B; if they are not, probably not.

Either way, even a court can't force a (distributed, non-centralized) blockchain to assign ownership of something to a entity B: it has to first find entity A and compel/force them to deliver the keys that control the assets, through the use of force.

> So the courts would be powerless to enforce anything on a blockchain, even if they wanted.

Even if that was the case (and, as I pointed out, it's not clear that it is the case... a court can always compel a person to give out their keys under the threat of force, as long as that person is within their jurisdiction, regardless of blockchain magic sprinkles), that would make blockchain assets more valuable (since that means they can't be easily seized from you against your will), and not less.

> In short, blockchains are designed in a manner that makes them antithetical to property rights.

[citation needed]

As far as I can tell, nothing in blockchains prevents courts from exerting their power within their jurisdiction. In fact, in some sense, it might make it even easier to do so: remember that transactions are irreversibly recorded (i.e. if the courts needs evidence against you, you would be better off having used cash than any blockchain asset).

> I think most people want property rights and therefore will steer clear of blockchains.

Blockchains don't remove or restrict your property rights; they just don't enforce or explicitly encode it, just like any other formal system or physical asset: you always have to rely on an external non-automated system of courts and law enforcement to ensure that your property rights. Blockchains don't change that, and are not supposed to change that, or to replace courts and law enforcement. So-called "smart contracts" are not actual legal contracts and shouldn't be seen as such. Etc.

TL;DR: It seems to me like you are postulating that blockchains need a feature that no other asset or medium of exchange has (i.e. automated enforcement of property laws, without having a court and a judge involved), otherwise it's not useful. If you apply that same threshold of usefulness to other classes of assets, then most (if not all) assets are useless (since they don't encode and can't enforce your property rights over it).