If, alternatively, you're suggesting that it's an error for parents to change their desires with respect to bearing the child once it's born, you may well be right, but in that case I have to conclude "I can't imagine why" was meant rhetorically.

More like I was assuming too much stuff in the implicit antecedent of the conditional whose consequent is “would want”, but yeah, what I meant is that it's an error for parents to change their desires with respect to bearing the child once it's born.