"There is no secular reason why every human life is precious."

Hogwash, Prager. When secularists want to do away with God's morals as having come from God, but want to keep the morals anyway, they often resort to evolution. "It's the preservation of the herd," they reason, "it's in our genes to protect every member of the human population so the next generation of humans can continue."

That's about it. Seems like a valid reason to me, if you're careful not to look too deep.