[Aquinasfan]

The sin of Onan was that he disobeyed God's command to procreate if memory serves. He spilled his seed on the ground to prevent procreation. It was not the act itself that was wrong, it was the intention behind the act.

That's a stretch, and an example of the problem with Sola Scriptura. How could every Christian denomination have been wrong until 1929? What happened? Could rationalization have been involved?

More on Onanism/Birth Control

[steve-b]

How could every Christian denomination have been wrong until 1929?

How could every Christian denomincation have been wrong about slavery until two hundred years ago?

[sauropod]

You are making this much more complicated than it needs to be.

God gave us freedom. When Man formulate straditions or strictures that are justified through a derivative argument, Man is taking away the freedom that God has given.

AFA your sarcastic point about every Christian denomination being wrong until 1929, I would argue that many Church practices (indulgences, others) may have been believed for hundreds or thousands of years. But if they are not specifically addressed in the Bible, then they are inventions of Man.