One of the dangers I can see is that their instances become supernodes that carry a lot more sway over the underlying AP protocol. They could use Microsoft's old "embrace and extend" philosophy and start making special extensions that only their nodes have. Then their critical mass either forces changes to the underlying protocol or bifurcates the fediverse into "Meta-based" and "not Meta-based".
Another issue will be what data they can mine from their users as well as other instances, and what tools they will build to circumvent any protections to mine all the fedi data.
And let's not even talk about the moderation issues (or sure lack thereof) that will make the fediverse much less safe for everyone. We've already seen time and time again that Zuck & co. don't care about moderation and user safety, and actually would rather manipulate data to their own nefarious ends.
There are so many more reasons why this is a bad thing.
Enh, government and business are so deeply in bed together that they might as well be one and the same in this case. Seems like a fit to me.