The Death of Onan

I would like to propose as a topic of consideration, that Onan, son of Judah, brother to Er; was not struck down due to transgression, but on account of vision. Consider, that at this time the people of Yaweh were but simple shepherds. Agriculture was not actively practiced or sought out, and the original farmer himself was cursed by god. Yaweh was not yet ready for his chosen people to cast their seed to the ground. It is only after finding the promised land, where they live by the fields and vintage that they are allowed to practice agriculture.
The true moral of the story here is not that coitus interuptus and contraception are aversive to god. But rather that seeing and actively attempting to cultivate a future that god has not attended is the aversive act.