A child in it's mother's womb is like a person hiding behind a door. To argue that the child is not in this world is to create a strange, solipsistic world-view.
A child hiding behind a door is aware of what he is doing. If he has the ability to hide he is aware of his existence and is able to function on his own. He may not see what is beyond the door but he knows something is there. A developing human in the womb of a woman has none of that awareness or ability. Of course that potential human being has value and should be honored as an expression of life. But in this human experience we have circumstances which are not ideal. We have to make difficult decisions and sometimes we get it wrong. As long as those decisions do not impact those who are already living and operating in this world (as war does) then it seems better to deal with the problems more immediate. Maybe if we solve those, the others, like abortion, will fall into their proper place.