an algorithm takes a selection of high ranking fb posts and cross-posts to Lemmy, far faster and more frequently than regular users. Oh, you’ll need to login to read.

So what? The Lemmy meme communities make posts way faster and more frequently than any other communities. Did I solve that by demanding my instance admin not federate with those instances or communities? No, I just unsubscribed from them.

And if Threads send encrypted / locked posts to Lemmy that cant be read on Lemmy clients then you just defederate from them then.

threads could wholesale repost other users and their comments, but behind a threads login wall

So? How does Threads forcing their users to sign in make your experience using Lemmy any worse?