Well, your argument assumes two falsehoods to be true. A) That a collection of human cells is a human being. B) That a fetus is separate from the mother in any way shape or form. Both are untrue, unless you avoid using logical, operational definitions to define what a living human being is, and instead define this in an arbitrary manner so that you can support your point. Furthermore, your arbitrary definition of what a living human being is will be contradictory if you are to assume A is actually true because the given collection of human cells will eventually become a human, because this would be untrue if B was true. Your argument is not one from science. Your argument has a mostly scientific premise, to which your implications are made specifically from the non-scientific parts of it. This is due to the fact that in practice, to classify something as a living, human being, we use a logical, operational definition which excludes any and all things that we cannot possibly consider a living human. We do this by understanding the differences between humans and other organisms or objects. One of the key differences between humans and other species is our cognitive abilities, which is a great place to start. If a being is incapable of conscious thought, withholding those which have previously been capable, then it is not a human being. The thalamocortical complex forms around 24 weeks into gestation, and renders conscious thought possible. Before then, it isn't a human. All of that being said, I understand that you won't coincide. I don't particularly care if you don't support abortion, I'm just explaining that this isn't a scientific argument you have presented, nor is it a logically sound one.