Athiesm has come a long way. It started with doubt of myths; Plato and Aristotle gave god a philosophical, non-human character. Epicurus thought there were gods, but only uncaring ones, and says that fear of gods is a chief misery for humankind. The Skeptics invented what we now call 'agnosticism'; essentially saying that we are unability to ascertain whether god/gods exist. Romans saw religion as a civic duty less so than a crucial soul-saving creed.
But movements toward unbelief in deities stalled following the conversion of Constantine. Athiesm withdrew into hiding, barely alive south of the Mediterranean. Paul and Augustine managed to make doubt part of Christianity itself; the goal was not to establish the truthhood of God, but to accept Him. Doubt was a torture that threatened the soul. Doubt outside this framework, threatened the souls of everyone.
Athiests had been persecuted and murdered up to this time---now they were hunted. The inquisitions held in several European nations killed not just writers and purveyors of doubt, but common people who independently wondered if perhaps they weren't getting the whole picture from the church.
Although the Enlightment came, there was still fear in the hearts of rationalists. But in the USA athiests had found a land formed by athiesm. (Paine and Jefferson were certainly unequivocable athiests, the latter being a devotee of Epicurus' philosophy. Franklin, for himself, claimed to be a deist. Those who claim that the US was created by christians with christian values are sorely ignorant.) Here cosmopolitanism and technological advancement were good to athiesm. Doubt became widespread. Feminists, railing for the vote and birth control, took up an anti-religious stance. Mark Twain wrote Letters from the Earth, taking cues from Paine, Thomas Huxley, and Darwin (the satire was all his). Freud wrote that religion was all a result of a desire for a father.
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There are two problems with the athiest movement today. One is that it comes with the stigma, placed on it largely during the 50s, as being the ally of the unbelievably disgusting communist regime of the USSR and the crazed and murderous progressivism of the French Revolution. During the McCarthy Era "In God We Trust" replaced "E Pluribus Unum"; "under God" was inserted into the very odd practice of swearing to a flag. Athiesm meant communism. This, I think, will fade with time, as the understanding of violence as a root cause of evil is seen as being uncorrelated with unbelief. (In the coarsest of analyses, how many repressive regimes can you name today that are theocracies vs those that are athiest?)
However, athiests, in their silence, are remiss. If the word that characterizes a generational ideal for the 1940s was 'duty', surely today the word is 'tolerance'. We tolerate anything that anyone wants to believe, be, or support. What does this lead to? How many college girls seriously and zealously investigate Wicca? How much money is to be had in tarot cards? How many times have we heard a sentence by fellow athiests start with "Look, if you believe in god that's ok, but..."?
Why is it ok? We live in a very successful culture of secular, rationalist materialism. The technology that makes our lives so enviable is the product of that philosophy, and it should be a ubiquitous reminder of that. The idea that science and God are mutually exclusive is incompatible with this philosophy. But do we press the issue? What about with friends and family?
Things like religion, horoscopes, intelligent design, environmental mysticism, Kabbalah, pseudoscientific self-help books, and outrageous urban legends don't just exist in our society---they thrive. It's sickening, and needs to be intellectually and civilly combated. So, please, those beautiful believers in free, rational thought, please publicly and privately disparage those who believe strange and highly contestable things. It will perhaps make you unpopular; that is historically the lot of athiests and free-thinkers. This unpopularity, though, entitles you to a place in the prestigious club of hated, wonderful, reasoning, right people, from Anaxagoras thru Cicero, Averroes, Spinoza, Hume, Rand, and Rushdie. Company like that, I can stand.