People aren’t against companies, people are against Meta. In the wider fediverse, anyway.
A while back there was talk of Tumblr potentially joining the fediverse, and it was met with neutral to positive reactions. No idea what happened there, maybe they’re still working on it, but I do not expect a “fedipact against tumblr” to gain as much steam (if any) when they decide to announce they’re ready to flip the ActivityPub switch.
(no idea if my other comment got sent out, this may be a duplicate)
There are signing keys involved, so if someone puts up a new server but uses different keys then all sorts of federation trouble will await them.
That said it shouldn’t affect the general network, just that individual server (both the communities and the users of it)
Edit: As for switching domains on an existing server, that would be equally troublesome as ActivityPub kinda relies on domains for all sorts of IDs.