I asked why viability matters, not why consciousness, breathing, or legality matter.
Consciousness has no bearing on what species an organism is nor is it a requirement for life.
Legality is a terrible and unscientific way to define what is alive.
The fetus is a member of the human species and they utilize energy, grow, and develop. By any Biological definition, they are indeed alive.
The inability to survive without attachment to the mother means the fetus is not viable, not that the fetus is not alive. Since they are already alive and obviously members of the human species, they are already human lives, not "potential" human lives. Their mortality rate has no bearing on this nor does it mean they are only "potential."