If anyone tries to make you feel ashamed, or inferior, or like your life will be dreary and intolerable because you don't believe in this lie they're telling you that's not OK.
Although it's Republicans who are primarily making the charge that atheists are un-American, Democrats aren't exactly lining up to defend non-believers.
If you look closely there are promising signs that American attitudes are changing in a way that may blunt the impact of religion on politics and culture.
The argument from utility -- the defense of religion, not because it's true, but because it's psychologically or socially useful -- is freakishly common.
Atheism is not just about disproving religious belief; it's also a burgeoning social justice movement intent on tearing down the social structures that perpetuate injustice.