I honestly don't know why you need religion to tell you that killing, stealing, incest and abuse are wrong.
That's an easy thing to say when you grew up in a civilization in which these things are viewed as pariahs. CS Lewis and other modern Natural Law theorists were right when they said people are aware of a moral code. They underestimated man's ability to twist and contort it over time.
All of these things, in different times and different places, were viewed either as a moral good or occasionally acceptable. Religion informs the culture, the culture informs the state. The state writes in law what is in the culture so as to punish evil and reward good lest the public err from that desired good.
A statesman is vital in the process of making sure that murder, incest, rape, etc. are still considered moral evils. Why? Because you are right, many people don't think they need religion or any ethical system at all. That is why an ethical system of some sort must be imposed upon them.
If you sincerely believe that allowances for murder, stealing, incest, and sexual abuse, you really are better off casting your lot in with evangelical Christians than almost every other political sub-group out there.
I say this as a Presbyterian (albeit a very conservative one) who cannot stand many aspects of evangelical churches today. Impose your lack of liturgy on me, then we're living in a theocracy...punks...
I'll give you credit, Nautilus. I like that you have such a fight in you. Though I sincerely wish you would take it and apply it in a different direction.