{ 1 } - Killing a fetus is not socially useful.
{ 2 } - Killing a fetus is socially disapproved.
{ 3 } - A fetus is innocent human life.

People disagree about whether a fetus is "human life." This isn't a factual dispute over when there emerges, in the same clear sense of the term, a "human." Instead, people use the term "human" in different senses.

The real issue is how we should take "human" in the first premise.