Others may have posted something similar but just as atheists who are liberal or Democrats don't necessarily endorse every element of the Democratic party, there are atheists who are politically conservative in some ways and even are Republicans. I see no reason to be in the "closet" on political beliefs while "out there" on lack of religious belief.
My atheist wife and I have many gay friends. We support a woman's right to choose. We are "liberal" on most social issues. But on the supporting the military, fiscal responsibility and keeping the government out of every element of our lives (not just the womb or our sexual habits) we are very conservative.
While I know other atheists (even a couple gay friends) who are vehemently conservative, most of my atheist friends find this hard to reconcile.
Bottom line is just because you don't believe in a mythical eye in the sky does not automatically make you more supportive of all liberal causes.
I just joined ACA (I'm a newbie) but the programming and discourse are awesome and I have to believe this organization is making a huge difference in people's lives as they wonder to themselves whether a lack of faith is rational. Keep up the great work!