Can you elaborate on how exactly maintaining your own site/blog/domain/presence etc is at odds with privacy advocation?
Content control, copyright and DRM are orthogonal to the issue of privacy.
Also I don't really understand the use of the phrase "the distributed internet" to distinguish from "silos" and "walled gardens." The internet is by design distributed. FB while being a walled-garden is still very much "on" the internet.
You can't publish your site/blog/domain/presence privately to your friends. That venue does not substitute for Facebook. When talk about replacing social media, we have to accept that most people don't want to share their baby photos etc with the world.
A website that any old person can access means it's a website that any number of bots can crawl over and aggregate. Now you're basically back where we started with Facebook.
I think it should be possible by leveraging public-key encryption. That's going to require something beyond Wordpress though.
The only way to ensure that your content doesn't get reshared without your permission is to create a tightly locked-down walled garden. If you're really worried, you need some sort of DRM too. And if you're really really worried, you need global laws that ban software that breaks DRM.
You can't have private, distributed data. You have to pick.