Gays are different, but they don't send the message that heterosexuals are mistaken about their sexuality. On the other hand, not only are atheists different, but explicitly or implicitly, they are telling the faithful that they're mistaken about a core commitment (for some the core commitment) of their lives. As the number of open atheists increases -- and this seems likely -- we can expect some religious to become more defensive, more strident in promoting their beliefs. They will regard themselves as under attack.
MORE: http://www.huffingtonpost.com/ronald-a-lindsay/coming-our-atheist-is-not-the-same-as-coming-out-gay_b_1577843.html