Let me preface all this by saying that I'm all for stem cell research. And I think that there isn't anything morally objectionable in using all the frozen unwanted zygotes before they expire. They would have died and been disposed of anyway.
But let me get this straight: A zygote isn't considered alive because it doesn't demonstrate all of the 5 criteria for life?
Well isn't the cell the basic unit of life? Isn't each and every cell of the zygote alive? So how is it that the unity of those cells isn't alive?
In time, the resulting organism will be able to demonstrate all those 5 criteria. Ahhh but wait, with time its no longer a zygote now is it? So I guess then a child isn't alive either till it can procreate, right? Hmmmm......isn't the spontaneous splitting of one zygote into two identical ones (you know when you get twins) asexual reproduction? Does that example meet that one criterion or not? Why or why not?Don't get me wrong. Its just not easy to brush off the point that some make about us squelching life when one teases apart a zygote. I really think they have a valid scientifically supported point that we are interrupting a life process.
But I also think all we can do is deal with the here and now. So to the one group: You're really not making a convincing argument, to me anyways, by claiming the zygote isn't alive. But to the other group: Yes we do have a living group of cells here, but its not a person.... and in all likelihood (in the case of the unwanted zygotes) no one would have let it proceed to that stage of development anyway. The reality is they are there, and I think that there'll be a pretty steady supply of them even in the near future. So it'd be less wasteful to harvest those cells and see what good can be done with them.