I am an atheist and humanist and am fairly public about that in my personal life, but I think that, at least here in the United States, remaining silent about your atheism in certain situations is necessary to remain in good standing with your co-workers and social contacts. US culture is permeated with religion to an extent that I hope is unsurpassed in other western nations. We have a reference to god in our pledge of allegiance, on our money, and in many other inappropriate places.
Many atheists go further than I do, pretending to believe in the Christian (or another) god and perhaps even attending religious services in order to fit in socially or to avoid persecution. In the US, persecution of atheists is usually limited to social alienation or minor aggression such as bullying, pranks, and vandalism, but deadly violence can occur when Christian or other religious extremists feel sufficiently threatened by someone’s beliefs, in this case someone’s lack of belief in god(s). For some reason, an atheist’s lack of belief in a god is very threatening to many theists, as if these people’s beliefs are so fragile that they depend on consensus to maintain them. In any case, social theism is a common practice even here in the relatively free United States, and it’s a matter of life and death to atheists living in many other countries.
I work in software engineering and although I work with mostly intelligent and well educated people, there are still many people at work who are both religious and conservative (meaning they want others to conform to their traditional views) and these people would take a dim view of me being publicly an atheist. While prayers and talk of god are rare at work, when it occurs, I feel compelled to remain silent. I won’t pray with the theists, but I also won’t walk out of the room. I just remain silent and consider it as respecting their beliefs. I really enjoy working at my current job and my future there might have a cloud over it if some theists in middle or upper management considered me an affront to their beliefs.
It’s funny that many of the people I work with know I’ve studied and am a great admirer of several eastern “religions”, including Buddhism, Taoism, and Advaita Vedanta. None of these systems are theistic and I consider them closer to philosophical worldviews than religions as most people use the word. But because most people in the United States don’t understand these systems and because these are widely considered established and respectable (if odd) religions, I am also considered acceptable (if a bit exotic or odd) if I am thought to follow them. Humanism, which I am fairly public about supporting, is looked down on somewhat, much more so if I call it secular humanism. Atheism, however, is in a class by itself. For most people, it sets you apart from the rest of humanity, and has a number of negative connotations. Most of all, in the United States, it is looked on by many as a threat to all that is American. Despite all evidence to the contrary, most Americans believe America is a Christian nation founded by Christians, and if you are an atheist, then for many, you are anti-American.
My friends and some of my co-workers know I am an atheist, but at work at least, we arrived at this mutual understanding by engaging in a little social dance. The dance consists in each person throwing out statements that are atheistic (or free thought) leaning but aren’t inherently offensive to theists. If the other person expresses disapproval, then you stop. If the other person approves, then you each proceed to get more and more explicit until one or both of you finally establishes that you’re both atheist or at least open to atheistic thought. By this method, I’ve found fellow atheists and free-thinkers at work. Since fundamentalist theists feel they are in the right and that their god is behind them, they tend to be very public about their beliefs, so you can just listen to people’s public conversations to see who would be overtly hostile to your atheism.
These little deceptions and silences add up to allowing atheism to remain a dirty word in public discourse. Those who care about true freedom of thought have a responsibility to rehabilitate the idea of atheism so that reasonably intelligent and well educated people see atheism for what it is, an age-old and philosophically respectable view of the world. I can’t afford to be an advocate for positive atheism at work because I am sole provider for a family of five (plus three cats), but I’m trying to take a more active and public stance for atheism in my personal time.