So the argument that cryptography shouldn't be used, because it is not safe
That wasn't the the central point. The central point was that encryption is appropriately applied to either personal records or contractually defined money where ownership is both nominated and distinct from possession. If, on the other hand, you encrypt an un-nominated bearer token, the encryption is redundant. All you're doing is obfuscating critical blockchain properties and adding a new layer riddled with toxic exploits. In Bitcoin, transactions can only be de-anonymised off-chain. In Monero, they can still be de-anonymised off-chain despite its encryption.
Now, if you think that the cryptography is not working then you shouldn't believe either, that the digital signatures of bitcoin work
Agreed. That's why its blockchain balances are transparent.
If something doesn't square in one place, it won't square somewhere else and a global awareness of the blockchain state can quickly come to a consensus over what's happening. When you've got a thick layer of obfuscating nonsense stuck between the blockchain and its users (keyholders or non-keyholders) all you have is confusion and - ultimately - nothing.