There's a concept called Embrace, Extend, Extinguish (seemingly coined, in that form, in a Microsoft antitrust lawsuit). Here's the Wikipedia page on it: https://en.m.wikipedia.org/wiki/Embrace,_extend,_and_extinguish
As I understand, people argue that Facebook/Meta, via Threads, will use this strategy in the long-term to either kill, or make effecitvely obsolete, the open technology behind Mastodon. If not that, then they could easily make the federation part of Threads buggy & unreliable, souring their users' opinions on the "fediverse".
They don't need to control anyone; they only need to host a majority of the userbase (by being the most popular federated site). And they're not starting from a user count of 1 or 10, unlike a lot of Mastodon sites.
Obviously, Mastodon & Lemmy, and the sites that run them, can keep chugging along just fine, but it's argued that if Meta makes their federation implementation sub-par (or otherwise sabotages it), it'll hurt the user-base growth of sites that use these projects (as people will see begin to see it as unreliable or what-not).
Is it as doom and gloom as people make it seem? Idk, I haven't had time to care.
Crashed for me, seemingly as it was loading the top image as the second image loaded in fine. (LG G8 (not G8X, etc.), Android 11, Boost 1.0.4)