His question conflates procreation and parenting. In the context of what he calls "natural marriage," he is essentially asserting here that every child deserves parents with different genitalia from each other. For procreation, of course neither is dispensable. That has nothing to do with parenting.
Any parent who doesn't adequately care for a child is dispensable irrespective of his or her sexual organs. Procreation begins and ends with a single act. Parenting involves creating a nurturing environment for a child, and *that* is what every child deserves.