That would be true, assuming that an embryo is actually a human being. Which is arguable at best. A ball of rapidly dividing cells does not a human make. It's hardly any more human than my liver. I'd be interested to understand the rationale behind endowing a cytoplast with human qualities, aside from the grasping-at-straws potential human argument. Then again, I guess that's why they don't like masturbation either. Damn the Pope.
Tell you what. Provide me a single piece of credible science that argues that the offspring of two human beings is ever anything but a human being.
Your liver is your liver and will never be anything else. Even if you die and it is transplanted to someone else, it will always be your liver and any capable laboratory student could identify it as yours with a DNA test. An unborn is undeniably a human being. Immature yes, but a human being none the less.
As for the tired old "potential" argument. It isn't even worth the effort it took you to type it out. Sperm and eggs represent "potential" life. Once fertilization is complete, however, that potenital has been realized. From the time fertilization is complete, you have a potential doctor, or a potential, baseball player, or a potential arsonist but you do not have a potential human being because the offspring of two human beings can be nothing but a human being.
The whole "masturbation" argument is pointless as well. It only illustrates that you don't have a very good grasp of basic biology. Alone, both sperm and eggs are of no more consequence than your toenail clippings. They are just cells from your body. Unique in that they only have a half set of chromosomes, but still just cells from your body that will be sluffed off after a given amount of time if they aren't used. Once fertilization is complete, however, neither sperm nor egg continues to exist as such but instead, a brand new human exists in their place.
Your argument fails on every biological level but don't feel bad, all pro choice arguments fail on every level. You could be honest and simply state clearly that you favor killing human beings for the purpose of medical experimentation or that you favor abortion because ou feel that women have the right to kill their children for whatever reason they may care to make up. My bet though, is that the truth of your position is too repulsive for you to articulate.