As I said before, sometimes the bible get’s things right with morality. But because there isn’t ever a valid reason for the bible’s morality; it’s only right on accident. Take Leviticus 18:17-18 for example. Let’s say you marry a widow and she has a daughter. Most of us can agree that it’s probably a bad idea to also have sex with her daughter. Or, if your wife has a sister, it’s probably best not to have sex with her sister. A rational reason to not do this is pretty obvious, it will create a lot of unhealthy tension and competition, and it’s very easy to abuse your position of authority as a step-father.
God’s explanation for these restriction, however, is a bit less lucid. God’s answer is, don’t do this, because!
Well, he does get a bit more detailed. For these various forms of incest, you’re not supposed to have sex with relatives for two different reasons. One, because they’re relatives. Two, because it causes dishonor. Okay, maybe I was right from the beginning—it’s wrong, because.
I can’t help but be reminded of the Euthyphro dilemma. Is an action good because God says it’s good, or is it good of its own merit? If it’s good because God says so, then God can declare murder good, and murder is good, but if things are good of their own merit, then God is unnecessary to understand morality. Of course, this isn’t a true dilemma, but the point is pretty obvious.
Apologists have tried for years to weasel their way out of this problem, but continue to fail. One of the more common responses is that morality is good because God makes it good, but God would only ever do good things, thus he would never say that murder is good. This argument fails because it requires “good” to be defined as “that which is good,” a useless tautology.