Christianity is, in fact, a religion by definition.Religion
A particular system of faith and worship.
Freedom of religion (or lack thereof, as in my case) is a key principle upon which America is built. Indeed, religious freedom is an essential cornerstone of any free and just society. As such, religion can not be used as the basis for laws in any free country. Furthermore, given the sheer number of religions and individual moral systems, the only truly just laws can be those that protect the individual's right and ability to pursue one's own morality. Laws governing vice restrict that right and, therefore, are inherently unjust.
That's my philosophical argument, anyway.