It’s only your weird interpretation of what he’s saying that undermines this though.
He’s saying systems where you could lose your life savings to a forgotten password are unsafe. This is clearly true. He hasn’t proposed a specific solution but I think it’s far more likely he believes in “use other systems” than inserting a back door into the system he’s identified as fatally flawed.
1) Bruce says systems that result in catastrophic loss from loss of a password are unsafe.
2) Reading at face value, Bruce's idea of a safe system is one where your passwords are recoverable.
3) Bruce knows that wallets are secured by asymmetric cryptography, not "passwords". Therefore, he must be simplifying for a general audience.
4) Reconciling the previous two points results in an argument for mandatory private key escrow.
It does not make sense that Bruce would advocate for mandatory key escrow, and yet, that is the logical endpoint of the argument he made in his tweet for supporting this letter.
Because it’s extremely consistent he’s arguing the system in question is fatally flawed and that he opposes it entirely. He doesn’t need to be advocating for some back door in crypto when “don’t use crypto” is a better simpler explanation of his position. I think his signing a letter that may argue for a ban of crypto is fairly consistent with this.
He’s saying systems where you could lose your life savings to a forgotten password are unsafe. This is clearly true. He hasn’t proposed a specific solution but I think it’s far more likely he believes in “use other systems” than inserting a back door into the system he’s identified as fatally flawed.