If we hold to this then abortion as a legitimate form of birth control should be okay until the fertilized egg has developed to a point where it begins to make it's own blood.
It is not an irrational position.
I think it is if you believe life begins at conception. If you believe life only exists when the body produces blood it would be later. If we don't believe life exists until "he breathed air into you" then it would be at birth.
Life began for each of us the moment He decided to create each of us, for us to interfere with His decision in any way is killing.
A non-implanted egg can only take two distinct paths:
1. It can die either naturally or through the use of some form of abortifacient.
or
2. It can develop and eventually be born.
So, it seems to me that the pro-life position MUST BE to never do anything that causes death to the fertilized egg.