I think it would be a real shame, and would fragment the fediverse as a whole - some of Beehaw's communities are some of the best on the Fediverse (and I really appreciate the work of the mods of communities on Beehaw), but the Fediverse / Lemmyverse is a lot bigger than just the Beehaw instance, and I really like being able to participate in communities from all over. Having to create accounts separately on lots of walled garden instances is probably not worth it, so I think it would make both Beehaw and the rest of the Fediverse weaker.
Overall I'd be sad about it, and discourage, but I'm sure the fediverse would live on despite it, in a weakened form.
Perhaps the real question is why would you consider doing that? It seems like a lose/lose for everyone. Would you be able to elaborate on what the exact problem you are trying to solve is? Perhaps the community could help you come up with a better solution.