I feel like this is a key point for the entire discussion. The legality of deliberately foiling lawful investigations is debatable, but protecting yourself against wild-west malware decidedly less so.

That being said - if it's all fine and dandy, I don't see why a Cellebrite-foiler couldn't be a separate app. Moxie (threatening to) piggy-back it onto Signal, purely because it's the app he controls, is a deeply user-hostile move.