All civil laws are an instantiation of SOMEONE'S morality. They are, by definition, putting the State's authority weild the sword behind someone's idea of what society "should" or "ought" to look like, and those are undeniably moral terms. The only question is whose morality those laws will reflect.
The only true morality is God's morality as laid out in Scripture. Looking to nature produces all sorts of perversions, since all of nature has been affected by the corruption of the fall. General revelation is not a reliable guide for establishing truly moral laws.
Civil law, therefore, should reflect God's revealed law as the only true and reliable morality. This conclusion is unavoidable for any Christian, in my opinion. The only questions left for us to debate are, "How much of God's law ought to be within the purview of the State to enforce, and how much left to the Church and/or the family?" and, "Is there any duty for Christians to work toward this ideal this side of Christ's return, or should we just let the State belong wholly to Satan until he is fully and finally defeated?"