Someone else is likely better suited to answer. I have never used Facebook. I suppose I am an internet dinosaur in a sense but I use(d) e-mail when I wanted to communicate and limited for the most part communications through that method.
Google scans every eMail to gather data. They don't actually read them but look for key words and before long because you mentioned going to that steak house, there will be popup adds for competitors or junk mail with coupons and so forth.
Political opinions can be manipulated just like our buying decisions of any product.