My opposition to Facebook joining the Fediverse, through threads, is that everything that Facebook touches, becomes garbage. Instagram was a fantastic photo sharing app, until Facebook bought it, destroyed the community, and then changed the app from photo sharing to video sharing. Most of the people my age were part of Facebook, when it was young, vibrant, and a network of friends of friends.
We chose to leave Facebook for a reason. We chose to leave Instagram for a reason. For the leeches to then come, and invade yet another space is frustrating. We made a conscious choice to break from our Facebook friends, and Instagram friends, and now Meta wants to invade the Fediverse.
For me, it's not about protocols. It's about their habit of invading and destroying communities. Twitter was invaded and destroyed. With Twitter's demise, I considered dumping social media, altogether. Reddit reacted so strongly to their own changes, because we have seen how badly Twitter is being treated today. Reddit doesn't want to allow that to happen to them. For clarity when I say Reddit, I mean the Reddit community, not the Reddit owners and shareholders.