It all depends on what you mean by “human life.” Obviously a human sperm and egg are not going to produce an elephant. So in that sense it’s “human life.” But in the sense that matters for the abortion debate–when does this collection of cells become an individual human being with a soul and all the rights of a human being–that’s a different story. As you say, the “infusion of a soul is another matter.” Exactly. And different religions have different beliefs concerning when that happens. And you are telling them they’re wrong, and they would say you are wrong.
No, the Catholic Church does not “tell them they are wrong” with regard to the exact time that a human body, created at conception, contains a soul. Rather, since we don’t know when God infuses the immortal soul, we err on the side of safety and consider conception to be the point at which protection should occur.
"For you created my inmost being;
you knit me together in my mother’s womb.
14I praise you because I am fearfully and wonderfully made;
your works are wonderful,
I know that full well.
15My frame was not hidden from you
when I was made in the secret place,
when I was woven together in the depths of the earth.
16Your eyes saw my unformed body;
all the days ordained for me were written in your book
before one of them came to be." Psalm 139
Scripture reveals that the human life in the womb is an individual person, known by God, with days ordained for them. Does it not seem prudent to protect what God has knit together? Who are we to make determinations about what day or week God sees a person in that unformed body?
Science shows us a collection of cells, but God sees a person.