No, absolutely do not run your own instance, that's absurd. That's like saying you shouldn't bother using email if you don't host your own server.
Your concerns make sense, they have complete access to anything you post and I can't imagine that any sort of messages are encrypted. That's just true. They could theoretically take your posts and sell them for profit, though anyone can already do that by simply federating with your server.
Anyway.
There's a limit. Just assume anything you post is not private for sure. I don't know if you can edit things, but I'd be shocked if it were impossible for an admin to. Maybe I'm wrong, they're such early software...
The good news is that in theory you should be able to migrate your entire account from the one you are on to a new one if you don't like the policy. Maybe? Not sure if that works yet.
But no, do not roll your own instance, that is silly and ruins discovery. At the same time be aware that the one you are on is ultimately owned by someone with the root password.
I wonder to what extent the massive imbalance in news coverage was simply super wealthy families handing journalists pre-written pieces so that laziness would dictate this result (rather than the journalists doing this naturally, although laziness is natural enough I guess).