Atheism is a religion and has been ruled so by the Federal Courts - as has Wicca. The ACLU only touts the alleged "separation of church & state" when it concerns Christianity.
It's only natural though since Wiccans and Atheists generally vote with the left, so the ACLU won't rain on their parade. Christians on the other hand (and I mean born-again Christians not "I go to church on Christmas and Easter" Christians) vote with the right.
That's my definition of Christian also.