The point is that there is no simple "pro life" or "pro choice" answer, and it really depends on the specific context.
"Quality of life" may be something that is in the eye of the beholder, because, after all, how do you define this quality to be sufficient? Where do you draw the line? Whether the child will be abused or not in the future etc., is hard to predict simply from this choice...even some women who wanted an abortion at a point in time and didn't get one later learned to love their child (furthermore, there are also cases where the reverse is true).
You are right, nobody really has a right to decide for the child. Maybe we all at least deserve a chance. There are so many happy and beautiful children in the world. But it breaks my heart when there is suffering. Thank you for your thoughtful reply.