This question has been asked by humans through out the ages. In modern history the nascent American democracy declared that it was possible for some people to be partially human and it took advantage of this belief to create the most profitable slave breading program of that period. While closer to our time in history the Nazi party in Germany reaffirmed this belief about a broader segment of society and proceeded to execute its plans to eliminate these supposed inferior humans one class at a time. It has advocates and followers whom still exist to this day in one manner or another. But even more recently in history the idea that there are people that are not exactly human continues to be perpetuated by institutions such as the New Black Panther party and The Nation of Islam via its most vocal advocate its minister Louis Farrakhan.
What do all of these have in common? They insist on denying the right to life liberty and property to people whom otherwise could have all three without the assistance or intervention of anybody else. So what could be worst than this? It is denying life, liberty and property to those whom are dependent on others. Let me paint for you a picture. Imagine your new born baby being torn from your hands and being murdered at the direct order of her other parent because according to that person she would not be able to contribute positively to society. Imagine that! Or imagine that you could at little or no cost to your self dispatch your elderly, wheelchair bound parents into a premature grave. Imagine that.
Now imagine that inside your home is the person whom one day will cure cancer or one day will terra-form the moons of Jupiter and Saturn except that he is unable to live outside your home for nine months. You invited him to live there but now realize that it was a mistake. Imagine evicting him from your home and watching him die on your porch. Imagine that. Is the new born baby human enough to deserve its life? What about your elderly parents? Are they human enough to deserve their lives? What about the Intellectual tenants that must live in your home for 9 months, are they human enough to deserve their lives?
These seem like utterly preposterous questions to ask, don't they? They do because anybody with half a brain knows that it is immoral for an intelligent society to euthanize its babies, elderly or its handicapped. To do so would reduce us to the level of base animals whose instincts to preserve their own kind has failed them. But today that is exactly what is happening everyday. Young men and women are told that it is okay to dispose of their unborn children. They are taught to distinguish sex from reproduction and are encouraged to do the first with no consequence of the latter, treating the purpose of sex, pregnancy, as an inconsequential byproduct. So what then, if not an unborn child constitute a human life? If we can rip a developing baby from it's first most natural home then what is to say we can't do the same of a newborn or a toddler, tween or teen? The handicapped and the elderly are also therefore at risk. This question will be asked because it needs an answer. So what will you answer to the question what constitutes a human life?