Imho the burden is on #activitypub developers and #fediverse instance admins to clarify to users what being active on these platforms means in terms of #dataprivacy and the different modes they can be used to find, link and interact with others.
In particular, the line "its the public internet, deal with it" is certainly not the whole truth. Public timelines is just one usage mode.
People are justified to be suspicious given #surveillancecapitalism
Clarity and transparency earns trust.