True, many people explain why killing is wrong from a religious perspective; for example, many point to the Biblical commandment that "thou shalt not kill."   Most Christians believe people were made in God's image and/or that people have souls, and that this gives people value. But does that imply, like some have suggested, that secular people have no reason to find value in human life? No reason to feel passionate about injustices? 

In a word: No. You do not have to be religious to value human life. You do not have to be religious to see the humanity of the fetus. And you do not have to be religious to be pro-life.  

Secular Pro-Life, on Abortion

When asked how they think most Americans feel about the abortion issue, 51% of U.S. adults say the public is mostly "pro-choice," while 35% say "pro-life." This general perception that the pro-choice viewpoint prevails contrasts with the nearly even division of Americans' actual views. The same poll finds that 48% of Americans call themselves pro-life and 45% pro-choice.  

Bottom Line: For several years now, neither the pro-choice nor the pro-life label has been dominant among Americans. Nevertheless, 51% of Americans perceive that most Americans are pro-choice -- slightly more than the 45% personally taking the pro-choice stance. Barely a third of Americans, 35%, think most Americans are pro-life, considerably less than the 48% who are pro-life.

(from the Gallup article, "Americans Misjudge U.S. Abortion Views")

The scientific evidence clearly indicates that a one-cell human organism, the zygote, forms immediately at fusion of sperm and egg. From a scientific perspective, this single cell is inarguably a complete and living organism; i.e. a member of the human species at the earliest stage of natural development.

Despite the clarity of the scientific evidence many people (including many scientists) find this conclusion difficult to accept; it seems absurd to call a single cell a "human being," and, consequently, many simply reject the evidence as irrelevant, and instead ask a different question: when does human life become valuable? Many who question the value of the human embryo accept that human life begins at sperm-egg fusion and that human embryos are organisms, yet insist that these scientific conclusions are irrelevant to any of the important social issues that turn on the question of when life begins. What is relevant, proponents of this view assert, is the question of when the embryo acquires "rights" or "value" or "personhood," and these more nuanced and less scientifically quantifiable traits are believed to accrue gradually over developmental time...  

Rather than linking human rights/value to status as a human organism (a status that is clearly achieved at sperm-egg fusion), many attempt to use a specific biological structure or function as the basis for human rights, with "viability" or the development of brain structures capable of supporting "consciousness" (including the conscious perception of pain) being the most commonly invoked characteristics. Yet both viability and higher neural function are fundamentally arbitrary...  

The problems inherent in using any aspect of brain function as the definition of human "personhood" can be illustrated by asking just two disturbing questions. First, if we assign rights based on brain function, how do we view the wide range of variation in brain function that exists among postnatal humans? Are we comfortable assigning human rights proportionate to brain function, with the intelligent enjoying greater freedom and privilege than the less intelligent? Most of us find this idea intuitively repugnant... 

What is the status of those individuals who are initially above the bar, but subsequently fall below it as a consequence of injury, disease or old age? What about those who are born with a genetic or  developmental defect that prevents them from ever achieving the minimum requirements? Are such individuals to be considered sub-human animals?...  

Inherent to the "social convention" view is the idea that "inalienable" rights (such as the right to life, liberty and the pursuit of happiness) do not exist at all, but rather are only a matter of social accord or contract. Those who have sufficient power to impose their views or sufficient influence over public opinion to effectively promote them are free to define human "rights" in any manner they choose.  Consequently, this view fatally undermines both the concept of human rights and the concept of personhood. If all rights are conferred merely by social convention, why should anyone have any rights at all beyond those they are able to acquire by persuasion, by purchase or by power? And if rights are exclusively acquired in this manner, it is inevitable that the clever, the rich and the strong will enjoy more rights than the inept, the poor and the weak... Arguments that human rights accrue gradually over developmental  time, based either on structural/functional maturation or on social convention, are both scientifically and logically flawed. Moreover, they defy our basic concepts of justice. Therefore, criteria such as viability and consciousness should not be used as a basis for deciding when a human embryo or fetus is the subject of human rights.  

CONCLUSION
Modern scientific evidence demonstrates that the one-cell human embryo, or zygote, is formed at the instant of sperm-egg plasma membrane fusion. The zygote has unique material composition that is distinct from either gamete. It immediately initiates a series of cellular and biochemical events that ultimately generate the cells, tissues and structures of the mature body in an orderly temporal and spatial sequence. The capacity to undergo development is a defining characteristic of a human organism at the beginning of life...  

Ethical positions that deny the personhood of human being at all stages of life are logically inconsistent and scientifically unsound, in addition to having significant, negative implications for the ethical treatment of all human persons.  

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