There are millions of eggs and sperm frozen in sperm banks throughout the world.
Everytime a man masterbates or a woman allows an egg to pass through her body naturally they to are killing cells that could become children. if you take this argument to a cellular level then you are accusing every man woman and child who has passed puberty of murder.
You cannot justify your accusation of murder by condeming people who destroy cells because you and most the worlds population are guilty of this.
On top of this you allow every human cell to grow into a human, then laborities around the world will be churning out more babies then Mcdonalds is churning out happy meals. Th world would be over populated in a matter of weeks and thus the end of the human race by starvation. You have just condemned the entire human race to death for its crimes against human cells.