Bill D, if I may wax even more pedantic, there is no actual Scriptural evidence that Onan practised coitus interruptus, although most scholars make this assumption .
As you say, he "spilled his seed upon the ground" but IMHO it is much more likely that he was on the receiving end of a hand job or a blow job from his deceased brother's wife. (Who didn't swallow, apparently). I mean, has anyone on this planet ever practised coitus interruptus? Again, IMHO, the term is a figment of some sociologist's imagination.

Whatever, the good Lord terminated him for his refusal to do it normally. Quite right too, he had it coming.

Murray