Interesting take on the matter. Right now, I'm not sure which way I sway, since there's valid points on both sides. On one hand, I'd hate to tolerate Meta, and I don't doubt they have some plan for trying to bend and twist the Fediverse to suit their own interests. But on the other hand, as of right now, forcing them to play by the rules of the open source software we collectively use is leverage against Meta, and allows us to safely access their content without having to download their apps.
Definitely going to have to think on this a bit more, myself.
Why does open source software have to do with anything? ActivityPub is a protocol. There's no licensing for it, any more than there is for HTML or POP3 or fuckin... I don't know... Jello shots? You just write your own software that adheres to the standard and BOOM Fediverse. The only "rules" to play by are the parts of the ActivityPub protocol that let you communicate between instances.
In other words, there are no actual rules that mean anything here. Meta's sole intent is to seep into the Fediverse like diarrhea into a bed while the drunken redneck idiot occupying sleeps off his whiskey dick.
You have to be willfully stupid to think they have anything positive to add to the world.