Assertion or Argument?

#1.) The ability of a woman to have control of her body is critical to civil rights. Take away her reproductive choice and you step onto a slippery slope. If the government can force a woman to continue a pregnancy, what about forcing a woman to use contraception or undergo sterilization?

The above is an assertion-- not an argument. If presented with this assertion as a persuasion for the pro-life view, I would simply respond by asking, "Why should I believe that illegalizing abortion provides a woman of a fundamental right, or her reproductive choice? Isn't her natural 'reproductive choice' the decision to have sexual intercourse or not? Isn't her natural 'reproductive choice' the decision to have protected sex if she does not remain abstenant, yet isn't in a place where she can raise a child? Give me some evidence as to why a woman has the right to brutally remove a living human fetus from her body." The assumption made in this "argument" (which is really an assertion) is that every woman has a natural right to an abortion, but it never provides evidence as to why that is true. Here is some evidence, however, as to why that is not true.
Pro-lifers will argue that the reason why abortion is a woman's right to her choose what she does with her own body is because the unborn fetus is not human. First, according to the law of biogenesis, an organism can only reproduce after its own kind. Dogs produce dogs, cats produce cats, and humans produce humans. Well, there are only four differences between an unborn human and a born human-- size, level of development, environment, and dependency. (We can use the term "human" for both the born and the unborn because of the law of biogenesis. If someone responds, "well, the unborn is not human." We can simply ask, "Well then, what is it?" The law of biogenesis explains that "human" is the only acceptable answer to that question). Anyway, is human, born or unborn, less human because of a smaller size, lesser level of development, different environment, or greater level of dependency? If the answer were yes, that would mean diabetics who are dependent on regulated doses of insulin are less human than non-diabetics, a person in one city is less human than a person in another, a four-year old is less human than a forty-year old because of the adult's more advanced level of cognitive development, or a 5'4" man is less human than a 6'9" man! I would say that most people deny the truth of those four assertions, so why is it that they illogically assume that those four differences make the unborn less human than the born?
The lack of proof for the assertion that the unborn are not human, and that a woman therefore has a fundamental right to an abortion, is what distinguishes the illegalization of abortion, or "the government [forcing] a woman to continue her pregnancy" from "forcing a woman to use contraception or undergo sterilization."