For argument's sake, let's arbitrarily choose a point for the 'first' appeal to worthiness as an individual human being, then see if this application might be better served if we reach backward toward conception.
We will take the beginning of sentience as our arbitrary start of worthiness. That beginning would be dependent on form and function regarding the developing brain and our application of typical activity for the early brain (if we agree on brain directed/connected activity of the body as earliest sentience, rather than awareness by the individual organism that it exists; even the newborn is not sentient by the second application of the term sentience). It is relevant to ask, "Would this brain and body connected activity happen if the other ages of the individual organism did not happen prior to the onset of our broad application of sentience?" No, if the continuum of individual life is interrupted prior to this nebulous sentience, the onset of brain-body activity would not occur. If the continuum is halted in such a way that the continuum of development cannot start up again, the later expected ages hallmarked by typical future form and function cannot occur, for that individual life begun at a known conception.
Choosing a different age (instead of some hazy sentience) as our starting point, if we interrupt the continuum development of the individual life in such a way that we prevent the maturing of human sex cells, the individual in question will not have the capacity to reproduce a member of the species, EXCEPT where cloning of the individual could occur. Why is that relevant?... It immediately calls attention to the genetic reality of an individual human life. Science can now remove the 46 chromosome identity of an individual life and insert that genetic complexity into a 'de-nucleated' female sex cell to 'copy' the individual human life from which the 46 chromosome data is removed, starting a new individual life but not continuing the previous individual life by that special conception. And this may be accomplished from any age of the individual begun at conception, once the individual's complete compliment of chromosomes is present! Zowee, that's some continuum!
What does this indicate?... That the individuality of the life conceived is established at conception and first cell division (or just prior to cell division since cell division occurs soon after the 46 chromosome compliment is accomplished). The goal of cloning, in reality, argues for the individuality of the organism at its earliest existence, and that's why scientists doing this stuff consider the individual life to have begun at conception. Any point following conception that one applies an arbitrary definition based on defining the individual by form and function speciously disenfranchises the earlier ages of that organism, disenfranchises that individual life.
I would ask again, is that what our nation desires, unencumbered exploitation of nascent individual humna life? I would also argue that to do such, cannibalizes individual human life in its earliest age along the continuum of its individual existence begun at conception.