Argue with Rev John Henry Livingston, not me.
He didn’t want a woman to marry her deceased husband’s brother, either.
The idea was that nuclear family lived so closely intertwined that it was incestuous for them suddenly to marry, and for existing children to see their aunt or uncle move into the place of a parent.
All the letters I read from 1800s refer to brothers-in-law and sisters-in-law as brothers and sisters. It makes it confusing until you get the family lines straightened out. But it was very common for an older sister to take in younger siblings to raise once they had a home of their own. So the siblings became much like elder children in the households.
Nahh, it bothers my sensibilities as well.
Besides, as an agnostic, I’m rather under-equipped to argue with someone who has dedicated his life to studying a particular faith.
Would make for an interesting conversation, though...