The use of human embryos or fetuses as an object of experimentation constitutes a crime against their dignity as human beings who have a right to the same respect owed to a child once born, just as to every person. This moral condemnation also regards procedures that exploit living human embryos and fetuses-sometimes specifically ‘produced’ for this purpose by in vitro fertilization-either to be used as ‘biological material’ or as providers of organs or tissue for transplants in the treatment of certain diseases. The killing of innocent human creatures, even if carried out to help others, constitutes an absolutely unacceptable act. 

Pope St. John Paul II, Evangelium Vitae