Above, beyond, and separate from any moral or ethical duty that atheists have to extend basic elements of tolerance and restraint towards the religious in a pluralistic society, there is a compelling, even essential, argument for an atheism of absence that is fundamentally an argument towards self-interest.
I once listened to a recording of a lecture by the New Age guru Ram Dass (né Richard Alpert) in which he was talking about the unfortunate tendency for people who have quit smoking or drinking to become dominated by that rejection, to become in a sense defined by their not-ness. One really can become dominated by the things one rejects, and it's a terrible way to live. As Ram Dass put it, "you die from not smoking."
One of the profound weirdnesses about militant atheism is just this kind of presence-through-denial, the absolute presence of religion within these atheists. Spending your time not believing in something is, well, odd. I have often said, and only partly in jest, that the advantage of atheism is that you don't have to get up in the morning on Sundays. The point is that atheism compels you to nothing. It does not ask you to serve. There are no sacraments and no sacred duties, no commandments, no elect to bow to and nothing forbidden to avoid. This is a virtue both in loftier philosophical ways (non serviam) and in the simpler graces of free time and free travel. Contrast this to, say, the apocalyptic and bellicose rhetoric of Christopher Hitchens, who writes as if atheists have some duty to oppose religion. The absence of belief and the absence of duty are symmetrical qualities.
Even aside from that more obvious notion of things that I don't have to do, there is the larger sense in which atheism is a nothing, a not-thing. Even the statement "I am an atheist" is perhaps more of a positive statement than I would like to make. But religion has compelled me to make it, and I do believe the path of conscience is towards a place where the default is, if not non-belief, than no statement about belief. Perhaps we're there now, but I don't think so. And, yes, of course, there are those who shamelessly insert their religion into politics, in defiance of Enlightenment values and the American character, and yes they have to be fought. That fight is irrelevant to the question of the existence or non-existence of gods or God, and the existence or non-existence of God or gods is irrelevant to that fight.
Not to belabor the point, but think about, say, an atheist convention. An atheist convention! A bunch of people sitting around not being religious! People brought together by their absence of belief in something! Spending money to hear speakers talk to them about how they can better be not-something and not-believe in the not-deity! Several fun-filled days thinking about God because you don't believe in him and think he's a jerk! What could it possibly matter to me if my neighbors go to church? What could I possibly feel towards them because of what I don't feel? How could a genuine atheism compel one towards anger or bitterness? No, what anger exists is anger at the God you say you don't believe in.
No. Atheism is not a project.It has no purpose. It proceeds towards no end. It has no meaning beyond the simplicity of absence. It has as little negative presence as positive and demands no philosophy. Sam Harris's life is dominated by religion. It's what he thinks about; it's what he writes about; it's how he pays the bills. He speaks all over the country about religion, he opines on it constantly, denying it is his constant endeavor. His intellectual and philosophical life could hardly be more centered around religion if he were a monk.
Me? I go weeks without thinking about religion or God. And why would I?