As you've probably heard, Threads (a fairly new social network from Facebook's parent company Meta) is testing integration with the fediverse. Depending on how you look at it, it's a great opportunity, a huge threat, or both!
Back in May and June, when Threads' first announced their plans, there were quite a few polls on Mastodon about people's reactions, most showing opinions split roughly equally. How do people feel today?
Your word choice is just bizarre. Nobody would be excluded, they'd only have to make a profile on a different, normal server. And nobody would be "hurt" by not having access to Lemmy's memes about Linux and similar stuff.
Except that theoretically my "All" feed would still be full of garbage-tier content that people typically expect and post on Meta's services, and that userbase with its same mindset would eventually spill over into the communities that I do follow too.
Your response isn't self consistent.
If they make a profile on a normal server then your feed will be full of that same content you don't want. You're trying to exclude users, not meta itself.
Besides, you keep taking as though they're federating with Lemmy. They're not, they're federating with mastodon. Having mastodon posts show up automatically in your Lemmy feeds is unusual. Kbin, maybe.