I don't think it is completely tangential, as this gives a rational basis for that decision: a zygote or a blastocyst does not meet the requirements for {a human life} as opposed to a {single\mass} of {living but not particularly special} cell{s}.
There's no need for such a justification. Whether or not the baby is human we have right to force her to continue to act as an incubator against her wishes.
Continuing beyond the point when you know you are pregnant is making a decision to continue. Further anyone engaging in protected sex should have all the equipment necessary for that protection on hand, whether it is night before protection or morning after protection, it should be there with the commitment to use it.
People have the right to change their minds. Whether protection was sought, used, ignored or failed makes no difference - we have no right to force a women to act as an incubator against her wishes.