The most salient difference is that, unlike physical traits, a person's religion can change – often not easily, but certainly more so than, say, skin color (certain celebrity examples notwithstanding) – and a child born into a religious family is not, therefore, guaranteed to remain religious (and certainly not guaranteed to remain in the religion of their birth). Bering notes, correctly, that religiosity is to a certain degree a heritable trait; while this is true, it is not nearly as strong a tie as his closing assertion suggests. A significant portion of today's nonreligious – including New Atheists, quiet atheists, and those engaged in milder forms of nonpractice – weren't raised that way. I also see a difference between this shift and the type of mass conversion that Bering notes as being a notably unreliable form of propagating a faith (citing the ever-citable Shakers who condemned/forbade sex in favor of an all-converts policy; one can imagine how this turned out, and one would be right).
Much as they might wish to be as persuasive as the evangelizing charismatics, the New Atheists' arguments are too bloodless to draw in anybody not already prone to walking their direction anyway. The growth in numbers of the nonreligious is not so much a result of Sam Harris' polemics, Richard Dawkins' press, or Christopher Hitchens' antics as they are a result of disenchanted individuals finding their own way to a nonreligious path. This is helped by living in, if not an Age of Reason, at least an Age With Reasons, meaning that those who seek a different/more empirical explanation for (insert your moral/existential question here) than the answer offered by the faith of their parents can find it without much effort. While these reasons may not always be satisfactory (and, on occasion, the seeker will be told that we as a species don't have a perfect answer for that question yet), they can often be as meaningful or more so than those offered by religion.
Most telling, perhaps, is that demographic data don't support this sort of hand-wringing. The 1990s saw dramatic growth in the population of the nonreligious, with that slice of America growing from 8.2% of the population in 1990 to 14.1% in 2001. While the rate of growth has slowed – the nonreligious made up 15% of the population in 2008 – growth continues, and there's certainly no indication that the reproductive tendencies of churchgoers are significantly cutting into that. Christianity, for one, saw a 10% drop in its share of the US population between 1990 and 2008, going from 86% to 76%. Most of this decline (and, I suspect, most of the rapid gain in nonbelief during the '90s) comes from the historic Mainline churches and the Catholics, while non-denominational Christians (including the strong block of evangelicals) have made gains, especially recently. I suspect the '90s saw a large "coming out" for nonreligious people who'd been practicing moderate religion out of habit/family obligation. We now have a better feeling for what percentage of the population is naturally low in religiosity. To the degree that religiosity is heritable, and given the past social pressures in this country, I suspect that many nonreligious lines "passed" as moderate religious practitioners until a time arrived when they could safely come out. A truer understanding of our equilibrium is being reached (and considering the slowing rate of growth in the nonreligious, I suspect it more or less has been reached for now), as people more openly identify with the labels that best describe their true nature.
I know this is growing long, but one last caveat. I do not equate "nonreligious" with "atheist" (nor should anyone), and I suspect that some of the New Atheists would be disappointed by the number of people abandoning traditional religion without picking up the banner of the proud heathen. As a quiet atheist, however, I am just fine with what's happening. I share some of the concerns that religion, preached poorly, can be damaging when it manipulates people's emotions and views of reality (see, Christianism). The increased viability of a nonreligious lifestyle will, in the long run, help our country diversify and strengthen. The more often frequently we can prove that the nonreligious can have successful lives, raise moral children, and generally not be the murderous, incestuous, dog-loving, Satan-worshiping scoundrels, thieves, and rapists that we are occasionally made out to be, the less power Christianism's self-righteous us vs. therm narrative has. I am a quiet atheist, yes, but I am "out" to all those who know me and any who ask, and I doubt my lifestyle is any more depraved than most. I take comfort in knowing that 15% of my fellow Americans are living similarly pleasant lives of nonreligion, and I don't think too many of us are worried about being out-bred; after all, I was born religious, and so were most of the atheists I know.
The Dish 