Larger groups don't act the same way as smaller ones.
If your sister dies tomorrow, you'd probably be quite upset.
If I die tomorrow, you wouldn't care even if you found out.
Consider that your roommate, parent, village member, whatever, finds out that you're gay. It's a small group. They have the information to know whether that getting out would be good or bad for you, whether you'd like that information to be disclosed.
On a global scale that discretion just doesn't exist at all. Facebook doesn't _care_. A random worker who sees that information doesn't _care_. The information can make its way to someone who _does_ matter to you (or at any later point suddenly you may matter to them).