I suppose that if you can define something narrowly enough you can make all kinds of assertions. The term parasite is often used in the broader cultural meaning of someone who takes advantage of you (the brother-in-law who mooches off of you for months), people who take welfare, liberals or conservatives (depending on your political bent), and certainly an unwanted baby growing inside your body can fall within the common usage of the term "parasite" since it gets all its nutrients from the woman and has not got the organs to live outside of her body.
Once the fetus is viable outside the woman's body then that's a horse of another color.
So, at this point, we have determined that you are unable to justify your position as you must use an inaccurate definition in an attempt to support it. Rather than use the word accurately, you must use a common, broad brush definition that might apply to anything. Typical. We are talkiing about ending human lives here. If you were in court, being tried for your life, would you accept broad brush definitions being used in an effort to prove a case against you? No decent legal representative would. If you can't make an argument that you would accept if it were being used against yourself, you can't make anargument.
Your reference to viability being the requisite to having the right to live is also wrong. (who would have guessed it). Consider conjoined twins. Very often, one lacks a vital organ. That twin lacks the organs to live separate from the other. They may not be separated, however, unless the shared organ is too weak to support both and both will die unless separation is attempted. The operation is in self defense of the one who has the organ.
Unless death will result, the twin with the full compliment of organs must share his or her "nutrients" and bodily resources with the other. Sorry mare, but the facts simply don't support your argument. They never have.
I suggest that you review the roe case as I doubt that you ever have. If you do, you will find that the justices said that a woman has the right to terminate a potential human life. They never suggested that a woman has the right to kill another living human being. I can certaiily provide plenty of credible science that states explicitly that unborns are living human beings from the time they are concieved. Can you provide any that suggests that an unborn at any stage of development is a "potential human life".
Roe was decided based on an incorrect assumption. Justice Blackmun acknowledged this when in his majority decision he said:
"The appellee and certain amici argue that the fetus is a "person" within the language and meaning of the Fourteenth Amendment. In support of this, they outline at length and in detail the well-known facts of fetal development. If this suggestion of personhood is established, the appellant's case, of course, collapses, for the fetus' right to life would then be guaranteed specifically by the Amendment. The appellant conceded as much on reargument. On the other hand, the appellee conceded on reargument that no case could be cited that holds that a fetus is a person within the meaning of the Fourteenth Amendment."
Justice Blackmun said explicitly that if the suggestion of personhood is established, then roe collapses as the life of the unborn would be guaranteed by the 14th amendment. At the time, no case could be cited that holds that a fetus is a person within the meaning of the 14th amendment. That is, no case could be cited where an individual was convicted of criminal homicide for killing an unborn. A large number of cases can be cited today mare and the question of personhood has been answered.
In this country, you can't even be charged for criminal homicide, much less tried, convicted, and sentenced unless you have, in fact, killed a person. There are a fairly large and growing number of people in prison today having been charged separately, and specifically for killing unborns. The question of personhood has been answered in spades and the justice who wrote the roe decision has acknowledged that if the question of personhood is answered, that the unborn would be guaranteed the protection of the 14th amendment.
Now do feel free to either prove that unborns are something other than living human beings, or that no one is in prison serving a sentence for the crime of criminal homicide for killing an unborn. If you can do either, you have the embryo of an argument. If you can't, then you have no rational argument in support of your position.