^ ya something like that, Steven.
The Hebrews didn’t have any ****in 401(k)s or Roth IRAs. There was no planned retirement, you worked until you were too old or inform to work and then your kids supported you. Old people without kids had nobody to support them. If a woman got widowed without kids, she wasn’t gonna remarry, so she was doomed to die. Alone. In the wilderness.
So this is how it worked for the ancient Hebrews. If you’re a widow, and you don’t have any kids, your dead husband’s siblings have to give you one. This means sex, yes. But this also means child support. This also means the kid is legally recognized as your dead husband’s, and will in the future exclusively support you, even though his brother was the biological father and even paid for the kid to be raised and for you to survive in the meantime.
Onan didn’t want to pay child support. Or he wanted his brothers estate. Or whatever. What we know for sure was that he didn’t want to sire a kid. He did, however, want to sleep with his hot sister in law. So Onan pulled out.
Today, we’d consider this a wacky arrangement. It’s sex with your sister in law. But we have welfare and our women aren’t chattel. Our society is fundamentally different. To them it wasn’t about sex, it was about supporting your family (even if family by marriage) in a host of ways, including the biological. Our culture descends from a stodgy and sexually embarrassed island of social darwinists so there is very little about this passage that makes sense to us beyond the spilling seed part.
So to the ancient Hebrew, it was exploiting a vulnerable person, a family member no less, to satisfy his personal desires at the expense of their financial and biological needs. And for that, Onan was damned. The passage isn’t really about sex at all, in a modern version it would be written about guys like the Sears executives stealing pension money.