Should they? The Wall Street Journal has a report on the attempts of various atheist organizations in the U.S. to make atheism more acceptable to the general public. Atheists are in many ways the least represented and most reviled minority in the U.S. with opinion polls consistently rating atheists as the least trustworthy group, below homosexuals and Muslims. The Economist noted in an article last year that only one U.S. congressman out of 535 would publicly admit to be an atheist, making him the highest-ranking politician to do so.
At the same time, atheists represent a fairly significant proportion of the population, though the exact figures depend on whom you count as an atheist. According to Adherents.com, if you count the people who put themselves in the secular, non-religious, agnostic or atheist categories as a single group, they would form the world’s third largest religious group. This is admittedly not entirely fair. The site takes pains to note that plenty of people in this category are theistic or spiritual but do not profess affiliation with any religious denomination. For many others, it would be more accurate to say that they are indifferent to religion rather than being non-believers and would not be interested in organized atheism anyway.

