That’s exactly this this lack of confidence that can undermine the web economy, according to some institutions.
And that’s why Brussels introduced new laws and new ways to do, like the right to be forgotten of the recent GDPR.
Basically, you can assume that companies also play a role in keeping all the data they can, because they’re lazy with filtering or deleting it, or just want to make accurate users profiles. If they want to take something down, they can. (That’s what YouTube and copyrights owners already do. For example, we could just employ the same tech for us)
Some data can also be fetched without user’s consent nor knowledge, that’s what was blamed on ad services, or FB who places its buttons and trackers all over the web.
Check out the Web of Trust scandal.