Corporations don’t just sit out on new technologies, and no matter how hard you try you can’t force them to. Defederating from Meta’s new project preemptively is naive, and will not do much of anything.
Protocols are going to be adopted by corporations, whether we like it or not. SMTP, LDAP, HTTP, IP and 802.11 are all examples of that. If it ends up that meta is able to destroy the fediverse simply by joining it, that is a design flaw on OUR end. Something would then clearly need to be different in order to prevent future abuse of the protocol.
FOSS is propped up by corporations. By for profit corporations. If you want to stop those corporations from killing projects, you put safety guards up to make sure that doesn’t happen. You don’t just shut them out and put your head in the sand.
Why will Meta care? To their large user base, they are on the “federation” and we’ll be the odd ones out. Their users won’t care either. They’ll just use it. And Meta can spin up any number of servers they want. Any company can.
They might not, and frankly that would be the ideal solution, wouldn’t it? They fork Mastodon, have their own isolated little universe, and we have our own little Fediverse over here. But the rumors swirling indicate that they do want to federate with larger instances that will be willing to follow their moderation standards and optionally take advertisements - I explain over here why that is likely the preferable approach for Meta.