That conservative backbencher who proposed to re-open the abortion debate in Canada by posing the question of when life begins has every right to pose the question. But, I say this for very different reasons. I'm pro-choice, but the question he raised is something I think warrants serious reflection for it is not just a scientific question but also a legal, philosophical and humanist one.
Science, we have come to realize, is a poor, low hanging fruit. Our long history of eugenics, racism, classism and charlatanism points to the fact that science is ironically without standards that would even rival the likes of legal, philosophical and humanist discourse where we at least have some vague idea of what values should apply - sort of like we don't know how to define "happiness" and "love" and "quality of life" but we know from experience when we hit upon their examples.
Science, by opposition, is an amoral, objective enterprise (by design) that is only concerned with knowledge acquisition. It is merely a tool, indifferent to human values and whether it is good or bad for humanity: who and what interests weld it is a very important issue (or should be) for these facts and knowledge of them should be balanced by our society's values (as the legal systems, and philosophical, spiritual and humanist discourse are tested and measured by).
Using science, we can make claims without any sense of irony, that single cells (whether protozoa or our own cells) are living beings. I don't know about you, but I don't get paralysed by questions of right to life when I shed dry skin and cut my nails, or suffer injury; the questions of whether it be good or bad for me and how I deal with it come into play and inform my actions.
Potentia, which are zygotes and embryos by definition, does not a life make. But that is not to say they don't deserve humane treatment. Accredited abortion clinics, our open and liberal political, legal and societal values and systems provide that humane assurance as far as humanly possible. Life and consciousness often appear cruel to us; mature and realistic reflection and decision-making are often our only means of dealing with flawed and imperfect situations and circumstances.
Science and idealism, by design, are not at all concerned with such practical and humane questions.