Reasonable explanation, except the "standard terminology" part. There's nothing standard about it, which is why context and elucidation are important.
While we may start with nothing other than our DNA in a single cell, we do not start *as* nothing. We begin as human beings.
It's hard to justify any such statment using "begin" without sweeping the whole space-time continuum thing under a rug.
Every society of humans has injunctions against killing other humans. While the expression of that value may vary, and while individuals may not know that they should not kill, it is a constant among rational humans.
It's a rare society that hasn't had allowances, and even incentives for killing other humans--war, duals, executions, self-defense, etc. You are very selective about what history shows to be stereotypical among human societies.
I suspect your true frustration is with this obvious fact.
I suspect that you don't really suspect that. And you'll find my frustration much relieved by recognitions such as the one you led with.
In order to support your view that embryos have no value, you must deny all value.
I never said that I didn't value embryos. Even so, this statement is false. Sounds like another example of poetry over substance.
I've been reading "What You Can't Not Know" by J. Budzewziski and find myself agreeing with him on the simple fact that we all do know that there are basic values.
The fact that every society has *exceptions* as to which humans may and which may not be killed actually supports the position that they hold the value that humans may not kill humans. I know that society will hold you responsible for killing a human, unless you follow society's rule for the exceptions. And, I doubt that you will get off on a plea of "I didn't know."
A simple Google search for the term "default position" will confirm the meaning as a standard term for technology, including the Dell computer, Windows XP and Netscape I'm using to type this post. And I assure you that Dr. Spitzer's terms are "standard" for ethics discussions.
"Begin" is another simple term. Each of the human embryology texts I have state that human life begins at fertilization. The more technical, medically-oriented will denote specific cellular structures that appear at the beginning of the individual human life.
All in all, you have not supported your claim that the default position for humans is one of no values. The "default position" for FR is not a blue screen or even the sign up page - log out and you'll see it. The default position for humans - especially any that you or I would feel the need to convince of our values - is one of a thinking, talking (and, in our case, typing), adult who notices patterns, has seen consequences, and whose thinking is affected by their environment as well as their genetics. It could be they are influenced by their soul, but I can't measure that, and have not made a strong point of claiming the distinction between the soul and the mind and body as influences for values.
Can you turn your point around and persuade me that values only exist for the one(s) who value, without denying that there are any values at all? Which, why, how do you know?