I don't really agree with this. The core behavior of Lemmy should be to make a reasonable effort to delete it, which as I've understood it doesn't really.

And you don't have to give people a false belief - the button shouldn't only say "Request removal of data from all Federated instances", but also add that "But keep in mind that it's not possible to enforce deletion from all instances in a Federated environment, and some instances may refuse to comply".

I think we should strive for privacy as much as possible, and by default the instances should comply. Sure, there's nothing stopping anyone from not complying, but that doesn't mean that we shouldn't at least attempt to do it.