i'm sorry but you're naive.
If I want to post something and I want people to see it and react to it, I will post it to the side with more people.
do you know how FB or instagram work? Do you think that when you post, your post reaches your whole audience? I believe you know how they work but for some reason you chose to ignore now.
My argument is that the fedipact, if executed as desired by the people running it, will defederate from Meta and anywhere that federates with Meta.
So now you have 2 fediverses, completely separated from one another.
So, you've read the history of XMPP. Did you understand what google practically did? Simply put, meta will create new features on top of activity pub. Open source activity pub developers will be in a constant race to adapt their own projects in a way that will be compatible with meta's project. They will have no voice but to follow whatever meta decides. Users will start getting fed up that their open source instance is not behaving as well as their friend's meta instance. People will jump project and/or when users are polarised, meta will decide that they had enough with activity pub. It doesn't cover their needs and they move to another completely closed project. Users again are forces to choose side and the open source community is just left with the project which they adapted in favour of meta, but now meta is gone because they were never in the same boat actually.
Staying away from meta is a decision in the basis of protecting the whole project. It is not because people don't want to be close to the users of meta. It is because meta is not here to promote the federated networks. It is here to make profit of it and they may even destroy it if they believe that this is the way to make profit. Siding with them is naive and will never bring value in the network itself.