The fedimint website lists debasement as a potential problem under their tradeoffs section. From what they say ecash's privacy elements make it difficult to audit.

I think the guardians can audit how many tokens they have created vs how much bitcoin they have, and they could publish on chain addresses so users could survey those, but users would still have to trust them that they didn't create tokens greater in value than the amount of bitcoin they hold.

Also: only guardians can create tokens (or at least they have to sign off on the creation) so if unbacked tokens were being created it would mean that the people you are trusting not to rug you are lying to you on another count.