Put a two-year-old out in the wild with no human intervention. According to the above statement, a two-year-old is not a human being because it can't keep it's own body alive for any significant length of time without human intervention, right? Conclusion: killing a two-year old is okay, correct? And don't give me the "artificial means" excuse. Either the child is capable of living without "human intervention" or it isn't. Don't impose a bunch of artificial conditions in order to find a loophole for infanticide.
Viability is the correct line because the 2 year old child is viable and deserves rights because it's viable fully developed but dependant. Embryos and fetus are nonviable because they need to use a viable cooperative person to create or build itself. The 2 year old is already fully created. The parents are guardians not owners of the child. People own their embryos in ivf clinics.