To legislate morality or any other Church doctrine would be to establish in pieces what may not be established in whole. Therefore, moral instruction should be left to parents, churches, and adult peer pressure. The State should confine itself to its chartered role protecting individuals' rights to life, liberty and property. It is mere coincidence if the State's protection (e.g. outlawing murder) happens to agree with some creed, religious doctrine or dogma.
Furthermore, I have no standing by which to prosecute an offense not against myself. Therefore, I have no standing to prosecute acts that transgress against God alone, nor does any other citizen. If omnipotent, God needs none of our "help" anyway.
Moreover, for Jews and Christians at least, God has warned us repeatedly (Deut 32:35 etc.): "Vengeance is mine, I will repay." This tells me that, though I may care enough about some people to inform them that their attitudes may be offending God, it's not my place to choose the time, place and method of correction. In fact, if I get in the way, I may even interfere with God's plan, and God may next be correcting me.
How many of you as parents have seen one child attempt to punish another for violating one of your rules? How quickly do you squelch that? The authority to enforce your rules is yours (and perhaps your partner's). You may even object to unrelated adults meddling. Thus it is with God and God's rules: It is the ultimate arrogance (and in one sense, it is blasphemy) for a mortal government to usurp God's role of judging God's rules.