God chooses to bless some marriages with children, and he withholds the blessing of children from some marriages. God does as he wills. He is the Author of life. He opens and closes the womb. He teaches us that children are his blessings. He does not give children to punish, but to bless. To argue, in a legalistic fashion, that God doesn't command married couples to have children and that it is not wrong to choose not to have children, challenging the traditionalist to prove the contrary seems to be an attempt to evade the fundamental issue before us: God is the Author of life. God chooses life. God gives life. All we can do is engage, as God has ordained, in the activity through which God engenders new life.
I won't rise to the bait to "prove" that God commands married couples to have children and that it's wrong to choose not to have children because these legalistic challenges move the conversation away from where it really ought to be grounded: in God's fatherly love for us in blessing us with children. Hey, you don't want it, that's your problem. You don't want kids? Fine. But God loves children. God blesses his children with children. God established marriage for the benefit of the children he gives. The fruitful womb is a reward, not a punishment. God opens and closes the womb. We're not in charge.