If it wasn’t clear before the Cambridge Analytica scandal came to light, it should be abundantly clear to any onlooker now:
Companies like Facebook make a profit by tracking your behavior online, quantifying it through ruthless algorithms and questionable business decisions, and working to sell you (in quantified data) to another company to target directly for advertising and “news”.
Let me absolutely clear about this point: they are not selling “data”, they are selling you. Every click, every search, every page view, every integration on every single popular site you visit, every sign-in or “create account” action taken via Facebook’s identity management (the ever-present “Sign in using your Facebook account”) – all of these build an incredibly detailed profile of your behavior. Facebook, its advertising customers, and other “research” companies (like Cambridge Analytica) know more about you than you consciously know about yourself.
If the above points aren’t presenting a clear enough picture, let’s make it absolutely explicit: companies like Facebook make a profit by knowing you better than you know yourself. Companies like this build incredibly detailed profiles of who you are with information that McCarthy-era intelligence agencies and rogue/vigilante actors would have killed to get a hold of.
If these violations of privacy don’t bother someone, then there’s nothing more to discuss with that person. It’s likely someone with such a lax attitude on surveillance of this scope and scale not only doesn’t care, but is likely complicit or an active accomplice to the increasing overreach of the broader surveillance apparatus. “Nothing to hide” only matters when what individuals aren’t hiding remains legal, free from scrutiny, or above challenge.
Personally, when the apparatus invariably turns its attention and barbaric ministrations on those very same people, all they’ll get from me is a cold shoulder and an “I warned you”.