Decentralized systems aren't a 100% solution for everything.
It just slows down, limits censorship and legal spying/datamining.
The way the world is swinging isn't going in favor of freedom either because of greed or control.
A Gnu social Instance can act badly for example look at mastodon.social privacy terms.
https://mastodon.social/terms
These rules permits legal datamining.

Here's a bit about datamining if you have time:
-The surreptitious assault on privacy, security, and freedom
https://media.libreplanet.org/mgoblin_media/media_entries/1529/144_7_gerwith.webm
slides:
https://mikegerwitz.com/talks/sapsf
-Corporate surveillance, digital tracking, big data & privacy
https://media.ccc.de/v/33c3-8414-corporate_surveillance_digital_tracking_big_data_privacy
-Data collection, psychographic profiling, and their impact on politics
https://www.youtube.com/watch?v=HUm9hV9KPy0&feature=youtu.be
-The Power of Big Data and Psychographics
https://www.youtube.com/watch?v=n8Dd5aVXLCc