I'm not saying such "extra-protocol" theft of coins is unlikely. I'm saying that it is possible to prevent them (eg I run the key generation algorithm in my head, memorize the secret key, then accept some coins at the public key). I don't place them in an exchange. The only way to get it is to kidnap and torture me, and the US police will try to prevent that from happening, and I can sue you for assaulting me.
The point is not that doing something like this is practical for anyone, it's that in that case, my coins seem to be backed by math and PoW (and the infrastructure that prevents people from getting kidnapped). Basically, it seems weird to argue that the USD is "backed by courts" by your definition because suing someone to get your USD back is only necessary because it's possible to steal USD from someone in ways it's not always possible to steal cryptocurrency from someone.
Also, by your argument, the USD is not fully backed by the courts either; I can steal your wallet, take your USD, sell them for gold, and then abscond to North Korea. Then there is nothing you can do to get them back.
Also I don't completely appreciate the name-calling - I find both cryptocurrencies and "traditional" currencies (monetary policy, how it's linked to state power, metallism vs chartalism, the historical gold standard) fascinating - and I expect we can have an interesting conversation about the latter (specifically, trying to rigorously understand how the USD gets its value) in good faith
