[Modernman]

If not human, what is it?

A potential human, given enough time and the proper circumstances.

On the other hand, you could argue that you were never and are not now human.

No one could logically argue that an adult human is not a human being. Reasonable people can disagree as to whether a cluster of cells qualifies as human.

despite your ignorance of the scientific objective fact of when human life begins.

Biology determines when life begins, but what constitutes a human being is a question for ethicists and philosophers.

[Campion]

No one could logically argue that an adult human is not a human being.

Of course they can. All they have to do is to draw that arbitrary line you draw at "sentience" ... somewhere else. After all, it's merely your opinion that a human being is defined by "sentience" (whatever "sentience" is ... do you cease to be a human being when you are asleep?). Someone else can have a different opinion. What makes yours more valid than his?

[MHGinTN]

You asserted (vacuously), "No one could logically argue that an adult human is not a human being." Ever heard of the SCOTUS Dred Scott decision? You might want to do a bit of reading before opening yourself up any further.

[hocndoc]

You forget that many people in the past have declared that adults of the species Homo sapiens were not human because their skin color was different, or their gender or ancestry was wrong, or their political or religious beliefs were wrong.

The quality that you value is sentience. You fail to define sentience, but, let's look at the embryo of the human being and the embryo of any other species. The human embryo is the only one with a potential for that special sentience that allows you and me to have this conversation.

On what basis do you kill the life of the member of the species that has this sentience?

For that matter, how well must that individual demonstrate his sentience in order for you to believe that he or she has the right not to be killed?

In your value set, do you honor the right not to be killed of the infant who still has only potential sentience -no self awareness or memory which he can later express to us - or the adult who is similar to the infant in function or expression of the quality of sentience.

How do you discriminate against one while protecting the others?

It is safer for all humans to protect their rights because of their species, not because of their level of function or appearance or age.