The statement that they are potential lives is incorrect. An embryo is already alive and, since it has continuity through time with an adult human being (obviously actual living human), it has human identity as well. Therefore, it is a living human being.
“Only one life can come out of this process” is also incorrect. This is like having 4 teenagers and choosing 3 of them to be shot, and then concluding that “only one adult can come out of this process, therefore the 3 teenagers are merely potential lives and can be destroyed”.
Why would inherent moral worth depend on the number of neurons or complexity of the brain?
I agree! I don’t think consciousness can be further analyzed or broken down into its constituent parts. It’s just a fundamental property of the universe. It doesn’t mean, however, that human consciousness has no explanation. (An explanation for human consciousness would be nice, because otherwise we have two kinds of things in the world: the physical and the mental, and none of these would be explicable in terms of the other, except maybe via solipsism.) Human consciousness, along with everything physical, is well explained by Christian theism, according to which God created the material world, which is inert and wholly subject to him, and then created mankind in His image. Man belongs both to the physical and the mental world and (s)he can be described as a consciousness made in the likeness of the Creator. Humans have/are a consciousness because God desired a personal relationship with them; for this reason they are not inert substances, but have free will.
@Gunnar_Zarncke
No, the process of experiencing is the main thing that distinguishes the mental (consciousness) from the physical. In fact, one way to define the mental is this (R. Swinburne): mental events are those that cannot happen without being experienced/observed. Mental events are not fully determined by the physical events, e.g. in the physical world there are no colors, only wavelengths of light. It is only in our consciousness that wavelengths of light acquire the quality of being a certain color, and even that may differ between one individual and another (what you see as green I might see as red).