It is always about having new children, it almost never is about adopting existing children into a loving home.
Why create new life when there is already plenty of kids existing who needs care and love?
This is just like atheism, a lot of atheists are far more sensitive toward the actual meaning of religion than religious people, I have seen plenty of religious people who don't seem to care about the actual religion, just the traditions or looking good, while atheists are more careful about not wanting to misrepresent/insult the religion.
Same here, the childfree people have already made their choice based on facts and beliefs, the opponents have not.