Joined Lemmy.ml because it was supposed to be a security, privacy and FOSS focused community
Yep that's the line the developers put up there to lure people in. It's mildly disingenuous at best. Having to copy a line from a document titled "The Principles of Communism" just to sign up should've tipped you off that something was a bit weird.
Join an instance that has more lax federation standards and subscribe to the ml communities you care about, or get comfortable with defederation and people from other instances discarding your opinions. It's a choice you need to make.