I guess this is the idea here that I don't understand. Where in the Bible does it say that contraception is a sin? Where does it say that married couples must produce children?
Don't get me wrong--children are a blessing to those who can accept them. But I can find no references that intentional childlessness is a sin.
Onan's smiting by God for "spilling his seed," the command to "be fruitful and multiply," the statement that children are like arrows, and "happy is the man whose quiver is full of them," condemnations in the Pauline corpus of sexual behaviors that exclude the unitive and procreative powers of physical intimacy.
Intentional childlessness is not a sin. Who said it was?