If the descentralization of social networks continue, we will have to prepare for the eventual rise of the instances wars, where people will start to fight about which instance is better and which one is weird to be in and so on, but that's for the future of us all.
Maybe curse me for bringing the idea up, could a Lemmy instance exclusively use Facebook’s login features? So that you have to use “login with Facebook account” to create a Lemmy user on the instance?
Oh god.
I don't think the Lemmy code base supports that yet, but adding OAuth support is a natural thing to do at some point. I guess if you were dedicated you could hack it together yourself in your own instance even now.