But an embryo occurs with fertilization. Your comparison regarding abortion has nothing to do with the release of sperm and unfertilized eggs.
I completely disagree......sperm have purpose and we do not know their level of intelligence. Eggs have purpose, and we do not know their level of intelligence. They are both God's creatures, and your arbitrary line drawing makes no more sense than the law as written by the Supreme Court saying that their line is correct and that before that time it is simply cells which cannot survive and are not human, the very same argument you are making. However, your opinion and my opinion where the line should be drawn matters little, because the Supreme court has determined a range where cells are considered a life and need to be protected. Doctrinally, The Catholic Church is opposed to artificial contraception and orgasmic acts outside of the context of marital intercourse. This belief dates back to the first centuries of Christianity. Such acts are considered intrinsically disordered because of the belief that all licit sexual acts must be both unitive (express love), and procreative (open to procreation).
So to make the distinction of drawing the line, it is clear that such is neither scientific or certain, and that in fact my belief that sperm and eggs are God's creatures and should not be destroyed is just as valid as your belief that life begins only in a fertilized egg as has been clear in many interpretations of the bible by the Catholic Church.