Dude, sometime around 2010-2014, FB was asking users for the email accounts of their friends 'to contact them on their behalf'. I may have the dates wrong, but I remember being pretty pissed at the time, as my so-called 'friends' were feeding them not only my email but other info as well through polls and stuff.
.
I never used FB at all - yet I was getting emails as described by author, but years ago when they pulled that BS. I'm on Facebook and linked to it without ever opting in, because of what my own friends/family/coworkers give them.