Possibly unpopular opinion: Fragmentation is good, as it means there are options for leaving a community behind. Fragmentation and competition are synonyms, and generally competition is good.
Lemmy definitely won't kill reddit the same way mastodon won't kill twitter, but I don't want it to. I just want it them to be successful enough to be a viable alternative when someone like Spez or Elon think they don't need to listen to their users.
I don't understand the point of doing so preemptively. Just make a standard set of rules. Defederate when someone breaks the rules. Keep it simple. No point of sending the message of "there is no value in integrating with the fediverse if you're a large corporation". Much better to send a message of "if you continue to be a bad actor, you'll lose out on the benefits of the fediverse"