There are many applications that only request logged in user’s name and email address to be populated in the registration form. I myself implemented this many times without “harvesting” anything else.
Having worked in growth before (not at Facebook), I can tell that you vastly underestimate the impact FB teams have on how/when/what/for how long/how many times/etc content is displayed to end users. This is absolutely not a neutral impact.
Are you a Facebook employee? Your justification sounds a lot like the internal propaganda that is being fed to employees. “Facebook is net positive”, “it’s just a tool”, etc