Exactly. Every legislator--every human being--operates from a belief system, be it Christian, Jewish, atheist, nihilist, environmentalist, etc. But I've never heard a general call for atheists to leave their beliefs at home and stop mucking up the political process.
There's a fundamental dishonesty here, and I suspect some people just plain don't like Christian morality. Which is fine. But don't pretend that when you take Christian morality out you're left with something neutral and pure. You're left with someone's morality--not the Christian's, but someone's.
But what about our freedoms? By giving the government power to legislate morality, you are destroying the concept of freedom. Absolute power corrupts absolutely, unless you are God (which the government certainly is not). At what point do we stop voting because the government knows better? American conception and protection of freedoms and rights are critical to America's success, prosperity and power. And that of its people.
Furthermore, there are many theological and philosophical and logical arguments against legislating morality. Without freedom, there is no good and evil. You can't help but choose good, so its meaningless, because someone else chose for you. Where's the value in your action? Where's free will? I like Judeo-Christian morality. That is the code I personally fllow, and I value it for what it does for me and for others who choose to follow it, and for making the world a better place (as I see it). People can have the same values and different priorities, right? So who is to say whose priorities are higher? You? I am sure there is someone who is just as religious as you, within your sect of Christianity (as I presume you are Christian), who would vehemently disagree with you over what are priorities. Which of you should legislate?
Socialism is a set of morality too (and I would hazard to say a religion, even though pinkos hate me for saying that). They shouldn't legislate their religion. We shouldn't legislate ours. We must legislate universal goods, like freedom, tolerance (though not love), rights and duties. Not individual codes of morality. Because I won't live in a Muslim or socialist morality in America (if I wanted either, I'd go to Saudi Arabia or Sweden respectively), so why should they live in mine?