You realize that just because something has technical tradeoffs you don't agree with doesn't make it a scam? It's like you'd label UDP a scam because it doesn't have packet delivery guarantees.

A common scenario for Fedimints is in places where there is not a sufficiently developed legal system where you can seek legal redress against a custodian. The idea is that if the custodians are amongst a group of people it's less likely they'll conspire together. Whether this will happen in practice is another question but there's no scam here.