Like most atheists, it really is of no concern to me what other people believe. If you do not believe in a god or heaven and hell in any form, then the question of what other people believe about god is as of little concern to you as questions about which sports teams they root for or what cars they drive.
If you are a follower of a theistic religion, however, you cannot help but feel part of a struggle against evil, and often that evil is personified as Satan, and non-believers or believers of other faiths can be seen as followers of that evil. Organized religions also need members to survive, to keep the institution going. So for members of organized religion, there is often a mandate to try and get other people to also believe, and thus we have revivals and evangelical outreach efforts and proselytizing.
But atheists have no organization to support and keep alive with membership dues. We have no special book or building or tradition to uphold and maintain. You will never find atheists going from door to door spreading the lack of the Word.
This raises an interesting question. Should atheists be concerned about religious symbolism in the public sphere such as placing nativity scenes on government property at Christmas or placing tablets of the Ten Commandments in courthouses, both of which have been the subjects of heated legal struggles involving interpretations of the First Amendment to the constitution? If those symbols mean nothing to us, why should we care where they appear?
In a purely intellectual sense, the answer is that atheists (and other secularists) should not care. Since for the atheist the nativity scene has as little meaning as any other barnyard scene, and the Ten Commandments have as much moral force as (say) any of Dave Letterman’s top ten lists, why should these things bother us? Perhaps we should just let these things go and avoid all the nasty legal fights.