I'm not willing to take that risk. If there is a child, you are killing it, whether or not you "know" that child is there. You "know" that there is a chance that a child has been conceived, and you are therefore willing to kill the child regardless of your knowledge. I suppose it's easier for some people to lie to themselves than to admit they are killing their child.
Then I guess you will just have to live with Abortion-on-demand then. If you can't differentuate between a doctor knowingly killing a baby and a pill that might prevent a pregnancy, we will just have to live with the status quo.