Confronting prejudice seems to be a matter of not just social norms, but of visibility, psychology, and choice.
On visibility, race and gender cannot be hidden, so they were confronted much earlier.
Homosexuality is easier to conceal, but hardly easy altogether; it came next.
Belief, however, can be the easiest thing to conceal, making it less necessary to confront.
Then there is how these prejudices tie into our psychology. Race was perhaps the easiest to confront on the grounds that it was justified partly a false scientific claim (that we are significantly different physiologically and psychologically), which was not too difficult to debunk, leading to the exposure of the fact that we are simply xenophobic. Our shared similarities across groups and differences within them helped to cancel much of this out.
Gender is more difficult to confront not just because there are physiological and psychological differences, but also because of the sharp duality most people see, not to mention historical and traditional roles and assumptions—many accepted or even embraced by many women themselves—making it harder to break through.
Homosexuality is tied to any number of sexual mores and bugaboos we still wade neck-deep in, and like gender, is tied to issues of control and self-identity, thus making it more difficult for some to break through.
Atheism, however, confronts some of our deepest fears: that of meaning, purpose—and oblivion. This connects to levels of suppressed horror and despair for some, which, even if subconscious (especially if subconscious!) are most difficult to confront.
Race, gender, and sexual orientation do have something in common, however, which sets them apart from atheism: choice. This is one thing that also delayed acceptance of homosexuality, that it was seen as a lifestyle rather than a permanent, set state of being. This still persists as a way for people to discriminate, because when it comes down to it, one of the best ways to justify a difference in human society is to demonstrate that the difference cannot be chosen or avoided, and thus demands equality on the basis of humanity.
Atheism, however, is in fact, a choice—mostly. Here, it is possible for one to truly convert as one cannot with race, gender, or orientation. I say “mostly,” however, because it is not always easy or even possible to change one’s convictions. For some, it is, but for others, it is so deeply tied to their self-identity that it is pretty much impossible.
All of these reasons explain why outright prejudice against atheists is still accepted.
Think about it: if Newt Gingrich had come out and said he would not accept non-whites in his cabinet, there would have been an outrage. Same for if he had said he would exclude women. Both may have been acceptable—or perhaps, politically survivable—statements more than half a century ago, but are utterly unacceptable today.
Had Newt Gingrich said he would not have any gays serving in government, there would also be public outcry against him. We still hear things like this, but they are now socially unacceptable; as gays come out of the closet, homophobes go in, to join racists and sexists.
But Gingrich did not say any of these things. He said, instead, that he would not accept any atheists serving in his administration.
Nobody even seemed to notice that he had said anything wrong.
And here, Gingrich even noted how it is easier to discriminate against atheists than it is to reject members of other religions:
Now, I happen to think that none of us should rush in judgment of others in the way in which they approach God. And I think that all of us up here I believe would agree. But I think all of us would also agree that there’s a very central part of your faith in how you approach public life. And I, frankly, would be really worried if somebody assured me that nothing in their faith would affect their judgments, because then I’d wonder, where’s your judgment—how can you have judgment if you have no faith? And how can I trust you with power if you don’t pray? Who you pray to, how you pray, how you come close to God is between you and God. But the notion that you’re endowed by your creator sets a certain boundary on what we mean by America.
In short, I can accept you if you’re a Mormon (he was speaking to Mitt Romney’s religion, ironically defining himself as tolerant), or if you’re Jewish, and even potentially if you’re a Hindu or a Muslim (though he would very likely escort such people quietly out the back door).
But if you’re an atheist? You’re damaged goods and have no place in our society. If you think I exaggerate, go back and read what he said again.
Following is a snippet of a discussion on this topic, which prompted this post.