Like it or not, our government does legislate morality. Outlawing murder, rape, theft, and fraud are to varying degrees moral statements codified in law.
While I think we can agree that a purely religious backing for these moral statements is insufficient for justifying laws, I'm not entirely sure what we think should be a sufficient condition for legislating a moral principle.
Does the majority determine morality? Do we base our determinations in utilitarian, puritanical, or deontological ethics?
Can banning weed be justified on grounds of moral purity? How about banning meth and heroin for the moral conviction that we don't want people to be hurt or hurt others?
If you believe abortion is murder, that would justify banning it without exception (except perhaps life of the mother) using the same arguments for banning murder itself. Who determines what the moral stance of the country should be on the issue?
Should we keep gay marriage illegal because many people deem it to be immoral on religious grounds? Probably not; but what about for a moral appeal to purity?
I myself disagree with most of these hypothetical laws and justifications I've proposed, but I'm not entirely clear on what principles I'm appealing to other than my own convictions on morality in order to make that determination. That would seem to put us back to square one with majority rules on morality. I'm not entirely comfortable with that.
How else can we (or should we) collectively determine the moral stances our government should take?
If you have any suggestions please leave a comment, because I don't have an answer at the moment.