What IS good, and how do we determine it?

[Randy Carson]

One might argue that God was simply angry with Onan for failing to honor a commandment to produce a child with his dead brother’s wife. But if you look at Deuteronomy 25:9-10, it is clear that the penalty for this failure is public humiliation, not death (the widow “shall go up to him in the presence of the elders, and pull his sandal off his foot, and spit in his face; . . . And the name of his house shall be called in Israel, the house of him that had his sandal pulled off”).

But that's not what happened. Onan’s actions evoked a much more serious response from God, and early Jewish and Christian commentators believed that by spilling his semen Onan had violated God’s natural law, the design he built into the human race, which led them to condemn the practice of birth control as being against God’s law.

I know the church teaches that.  It's the standard Catholic defense. 

Thank you. I'm pleased that you know I'm not simply making this stuff up.

But there are two problems with it.  First discharge of semen outside a vagina is discussed as unclean in Leviticus 15.  The penalty is not death but two turtle doves.  It's considered unclean not a crime.  It's treated as ritual impurity like menstruation which is discussed immediately afterwords.  So spilling seed is discussed as an impurity in Leviticus but no where in the law of Deuteronomy.  If it were a major crime that would be very odd.

Levitiicus 15:15-18
 If a man has an emission of semen, he shall bathe his whole body in water, and be unclean until the evening. 17 Everything made of cloth or of skin on which the semen falls shall be washed with water, and be unclean until the evening. 18 If a man lies with a woman and has an emission of semen, both of them shall bathe in water, and be unclean until the evening.

Jenny, I think there are two possibilities that you are failing to consider.

1. Wet dreams (very common - even among married, sexually active men), and
2. Premature ejaculation (which is unintentional).

In either of these cases, there would be NO culpability for sin, but the law still required ritual cleansing, etc. And in the case of v18, God is simply commanding that a couple take a bath after sex. Hello? So, the man was unclean "until evening"...a minor deal and not worthy of death.

Clearly, Onan was guilty of something far worse.

Second, Onan didn't just violate the Leverite marriage obligations he did so after being asked to do so by his father.
Most of what the Catholic church relies on for prohibiting birth control is it's own idea of natural law. 

Well, first of all, Onan DELIBERATELY spilled his seed to avoid having a child for his brother. Therefore, there WAS culpability because unlike the cases I've just discussed, it was NOT an accident or the result of a completed sex act.

The Hebrews may have thought differently.  Just for fun read through The Song of Solomon.  Much of the gifts he offers his lover were used in ancient times as birth control, specifically:  pomegranates, wine, myrrh, spikenard and cinnamon.  Somehow I don't think that was an accident.

Ah...so YOU can read the scriptures as YOU see fit, but I cannot quote the NT as I see fit? Kidding...just kidding?