My point is that condoning actual murder for the sake of “practicalities” is generally not something that anybody is willing to accept when it comes to the lives of fully human persons.
Well, if we really believed that a fertilized egg was really equivalent to a fully human person, the alternative we would choose would be to ban not only elective abortion but any type of birth control that performs its function by occasionally killing fertilized eggs.
We would end up with lots more unwanted pregnancies that way, but in the case of fully human persons we don’t let that kind of trade-off affect our stringent prohibition on murdering people.
For example, many Americans agree that it would be a good thing to have effective border security, because we don’t want people from other countries immigrating into our country without legal permission. Nonetheless, when some immigrants sometimes manage to evade border security and enter the country illegally, it is not legal to kill them in order to get rid of them.
But that’s exactly the sort of approach that you’re advocating in the case of fertilized eggs: Do your best to keep them from entering the system in the first place, but if some of them do enter, it’s permissible (albeit regrettable) to go ahead and wipe them out.