Facebook builds shadow profiles for people that don't have accounts. I have a dormant account and checked out my profile and they've linked together multiple email addresses I've never given them. Ad blocking and tracking protection aren't sufficient because retailers give data to Facebook. There are ways to delete data now, which is a welcomed improvement, but that's after it's already been collected.

With that said, I understand the larger point you're making about government surveillance. I just don't see most people being able to opt out of Facebook. Moreover, the government can compel Facebook to hand over whatever data is provided by users voluntarily, making the private/public split less than airtight.