Sometimes atheists stay closeted to avoid offending people; other times it's because you think the term "atheist" means you're a bad person. Sometimes it's to avoid losing your job; other times, your very life. This Washington Post blog article shows the seven countries where you can be executed for being an atheist. Things have improved considerably in the West, but there's still a lot of work to do - at home and globally.
Recently I posted at Reflections from the Other Side on one of the problems of implementing rational behavior when your strategies have to work within a game with irrational players. (This is called "real life"; expanded post here.) One of the problems is that if you're surrounded by people who declare allegiance to some belief (whether or not they actually behave accordingly), you can choose to openly defy the convention and probably be penalized, or you can keep your mouth shut or go along with it, avoiding near-term penalty but reinforcing the behavior. This suggests that a large number of people who are going along with irrational beliefs don't actually believe them, but they keep their mouths shut because they don't realize everyone around them is doing the same thing.
On a Friendly Atheist article about the Seven Deadly Countries (deadly for atheists that is), Hemant Mehta points out "In all seven countries, there are undoubtedly a large number of atheists pretending to be religious — or discussing their atheism only in the most discreet of ways — so they can live without fear of being captured and executed." Once people do discover that in fact there are lots of other people playing along and can declare their true beliefs in full view of others, there is often a dramatic preference cascade, which is one reason why revolutions in autocracies can happen so quickly.
This may be why the internet has been such a bad thing for Christian privilege in the U.S.; you might have been the one actively non-religious person in your town that you know of, but suddenly there's a way to find the others, and speak your mind. (It's even happening with professional clergy who suddenly realize they're not alone in their doubts.) Those preference cascades are held in check as long as people risk being tied to the utterances and killed. We should be working to find ways to let people in the most anti-atheist places find ways to safely express their ideas so that like-minded people know they're not alone.
USA PATRIOT Act
58 minutes ago